Clean Code - Uncle Bob / Lesson 1

[Music] for such an ambition we need the right skills and as developers we code so let's sharpen those skills and start coding a better world together [Music] this first edition of coding a better world together is on clean coding and clean architecture and who better to teach us more about this than mr. clean code aka Uncle Bob the one and only Robert see Marquis [Music] and here are your hosts for today [Music] Ahrens clubbers and fedoras mice the next which will be Uncle Bob I will introduce him Uncle Bob has an impressive career in the IT industry he has been working there for more than 40 years he always had a keen eye for what makes a developer a good developer he shares his fuse as often as possible and he will do that here in these coming two days also he is one of the authors of the agile manifesto and the manifesto for software craftsmanship he hates it that that agile movement has been taken hostage by the consultants and conference organizers with that they abandoned the programmers and by abandoning the programmers they abandoned the values and discipline of craftsmanship and I think that's a very very sad message but Uncle Bob stays positive and he keeps sending out that message of craftsmanship so please welcome Robert C Martin better known as Uncle Bob [Music] [Applause] [Music] okay hello I'm Bob and by the way thanks to everybody who brought me in here that was awfully nice of you it's a pleasure to be here thanks to rob a bank and everybody who who made this possible special thanks to shirt from wanna flex she was kind of the catalyst for this entire event how many of you are programmers see you are my tribe I don't care if you're young or you're old or black or white or a man or a woman I don't care who you like or who you love if you are a programmer you are part of my tribe you and I and we all together share a passion for something and we can communicate it about it in a way that most other people can't and so that's something that we should cherish together how far away is the Sun five why do people know this and and it's as in it's a strange thing tonight I said five minutes you meant five light minutes the actual number is eight light minutes but why would you care how many light minutes away the Sun is does someone know it in kilometers or miles how many how many kilometers away is the Sun good 150 million kilometers that's a more human measurement than eight light minutes good of course if somebody is eventually going to say it's one astronomical unit and thank you for that how do we know that the Sun is 150 million kilometers away somebody read it in a book or something is it so who is the first person to calculate the distance to the Sun this person lived 2,500 years ago his name was Aristarchus and let me show you the technique he used because it's a fascinating technique oh my goodness I get a couch to sit on in everything hmm now let's see here's the Sun here is the moon and here's the earth and this line right here is the line that divides I should probably do that the other way I shouldn't the the line that divides the night side of the moon from the day side of the moon now if you are standing on the earth and you are looking at the moon and you see that the moon is exactly half phase then you know that this angle is a right angle if you could measure this distance the distance from the earth to the moon and if you could measure this angle right here then you could calculate the distance to the Sun because you'd be trying to calculate that side of the triangle now this angle here we can measure because you can get outside and see the moon in the sky and the Sun at the sky at the same time she might as well measure that angle and then the problem is to measure this distance here the distance from the earth to the moon we'll come to that in a minute Aristarchus did these initial measurements and he got the angle measurement off by a factor of 10 which made his whole his whole calculation off by a factor of 10 although that's actually not bad because you can imagine 2500 years ago he didn't have an awful lot of instrumentation to measure that angle and how do you measure that angle you have to find the exact center of the moon and then you have to find the exact center of the Sun and it's difficult to stare at the Sun for any length of time to find the exact center and then you have to measure the angle and it's a very very tiny angle it's actually a very close to 90 degrees the difference from 90 degrees is about point 3 degrees and he couldn't measure that that precisely so he actually measured 3 degree difference he thought it was 87 degrees but then he went ahead and did the rest of the mass now how do you find the distance to the moon well he reasoned this way here's the Sun here's the earth here's the moon at the moment of lunar eclipse the shadow of the earth is covering the moon the shadow of the earth is roughly the diameter of the earth the size of that shadow is roughly the diameter of the earth how long does the moon spend in that shadow well he measured that time to be about three hours how long does it take the moon to make a complete circuit of the earth well that's close to 28 days so that gives you a nice ratio it is the ratio between this the Earth's diameter and the circumference of the moon's orbit from which you can calculate the radius of that circle and get the distance to the moon in earth diameters so now we need to know the size of the earth now Aristarchus did not know the size of the earth and he didn't bother to calculated it was another Greek who calculated the size of the earth and his name was Eratosthenes about 30 years later and he reasoned it this way he said all right look here's the earth here's the Sun and a stick in Alexandria Egypt on the first day of summer at noon will not cast any shadow the Sun is perfectly overhead but at the exact same moment 500 miles away in the Egyptian town of Memphis the stick casts a shadow of seven degrees he measured the distance by timing the trip on a camel now it's pretty easy to do the math 360 divided by seven times 500 and you get the circumference of the earth you divide that by PI you get the diameter of the earth you plug that into the lunar equation to get the distance to the moon you plug that into the solar equation to get the distance to the Sun and Aristarchus calculated that the Sun was 10 million miles away 15 million kilometers away so he was off by a factor of 10 that's not bad for some guy 2500 years ago without any instrumentation that is the power of human reasoning he just studied the situation long enough and gathered enough data and came up with a pretty good answer his answer his solution to the distance of the Sun was not battered until 1630 so for 2,000 years that was the best measurement we had of the distance to the Sun and even back then it set the scale for the solar system in a way that nobody had expected of course this is not what we're supposed to be talking about is it right we're supposed to be talking about clean code so let's talk about clean code this talk is clean code and I have you I believe for for two 90-minute sessions on this topic so we ought to be able to cover a fair bit of ground here and I'm not going to go through that I will go through this this is a cartoon I found in a magazine several years ago and I thought it was particularly poignant the only valid measurement of code quality is WTFs per minute coming out from behind the door where the code review is taking place and you look at the code the door on the left and you realize that's probably pretty good code because there's not that many WTFs coming out from behind that door on the other hand that door on the right must have some pretty bad code behind it because there's a whole bunch of WTFs coming out from behind that door what we are going to be talking about over the next several hours is how to get behind that door on the Left how are we going to make our code good enough to survive a code review such that our peers are not tearing their hair out trying to figure out what the hell our code does why is this important how many computers are in this room right now thousands good answer how many computers do you have on your body at the moment now I can do this count with me I have my iPhone how many processors are in here eight you think is it eight I don't know how many it is there's the main processor in the screen processor and the Wi-Fi processor in the GPS processor in the Bluetooth processor it's got to be a bunch of others I don't know there's a bunch of processors sitting in here I am holding in my hand an amount of computing power that exceeds the computing power of the world in 1980 which is pretty interesting and you know we all have one and what do we do with it we play Angry Birds right which if you think about it it's pretty cool Angry Birds that's a great program virtual reality and everything right on the screen got some more processors on me let's see I've got my earbuds hmm how many computers are in here well there's one for each air but and the case has got a computer there's least three in here what else do I have on me I've got this microphone thing you think there's some processors in there I think probably it's probably a processor in there so on my body I have several dozen computers just working away helping me give a talk now look around the room how many computers are in the walls and the ceiling this cameras up there I got to have processors in them there's these lights here I imagine there's processors in those because looks like they're robotic and oh Jesus there's stuff on the ceiling I don't know what it is if probably processors in it there's the speaker's the speakers have computers in them nowadays it is cheaper to put a little digital signal processor in a speaker or a microphone and filter out 50 cycle hum than it is putting an inductor and a capacitor in there and that digital signal processors got some C code that does fast Fourier transforms and is written by some 22 year old at 3:00 in the morning got speakers and microphones got smoke detectors get signs yet exit sign there there a processor in that exit sign does it have a battery in it is that battery being charged is there a little processor sitting there monitoring the trickle charge going into that battery how often do you interact with a software system no no not you how often does your grandmother interact with a software system if you have a grandmother but how often in our society today it is impossible to go more than 60 seconds without interacting with the software system because there's nothing you can do in our society without interacting with the software system you can't talk on the phone you can't watch TV you can't microwave popcorn you can't wash the dishes or your clothes you can't dry your clothes you can't drive anywhere without interacting with the software system how much code is in a modern car how many lines of code in a knot a Tesla a Tesla's way over the top just a normal old modern car how many lines of code are in that it's over 100 million you get into your car you start to drive there's a hundred million lines of code executing in that car most of it of course is in the entertainment system and the GPS system and all that nonsense but there's a fair bit of code running in the engine when you put your foot on the brake do you believe that there's a cable that runs from the brake pedal to the calipers that squeeze on the disk or do you realize that there are if statements in the way and who wrote those if statements if statements that are going to decide whether or not to stop the car when you push on the brake how many people have died because of failures in those if statements dozens there are dozens of people who have died in automobile accidents because the software that controlled the brakes in the accelerator failed for some stupid reason you and I are killing people now we didn't get into this business to kill people most of us are programmers because one day we walked into a store and we saw some dumb computer on a rack and we typed five lines of basic to put our our a print statement that printed our name into an infinite loop and we saw our name going up the screen or what yeah that's what I want to do for the rest of my life but now we're killing people we didn't want to get into a business where you could do that not only can you kill people with software you can lose massive fortunes who knows about night capital who's heard about the fiasco at night capital about six years ago right I'm not going to go into all the details just some some guy made one dumb mistake and it was just a little dumb mistake but he managed to lose 450 million dollars and 45 minutes our society runs on software nothing happens in our society without software nowadays didn't used to be that way wasn't that way in the 1960s wasn't that way in the 70s wasn't that way in the 80s but today our society runs on software there is nothing you can do without software you cannot buy anything you cannot sell anything you cannot pass a law you cannot enforce a law you can't get insurance policies you can't get claims from insurance policies you can't get money out of the bank without software software runs everything and our society does not yet realize just how deep engine it is on software you and I probably don't realize it very well just how dependent everything is on software and who writes that software we do we rule the world other people think they rule the world then they hand those rules to us and we write the rules that run in the machines that govern everything we need to talk to people about taxes now since we rule the world seems fair that we shouldn't have to pay any taxes but we'll come back to that later does society understand just how dependent it has become on us answer that is no not yet although there have been hints there have been moments when we thought maybe society would wake up to this fact the events that will eventually of course cause society to wake up is when some poor programmer does one dumb thing in and kills 10,000 people at a shop and it's not hard to imagine what that would be all right you think for a few minutes you'll realize that it's about seven dozen ways you could kill ten thousand people with a little software failure and when that occurs and you know it's going to occur at some point in time some poor software idiot is going to do some dumb thing and kill 10,000 people and when that occurs the politicians of the world will rise up in righteous indignation as they should and they will point their finger right at us and you might like to think oh no they're not gonna point their finger at me I'll point my finger at their finger at my boss or my company cuz it's not me but we saw what happened when the CEO of Volkswagen North America testified before the American Congress about why the software in Volkswagens was cheating the Environmental Protection machines in California and the Congress asked that CEO how could you have let this happen and the CEO answered and I quote it was just a couple of software developers who did this for whatever reason unquote now he was right it was a couple of software developers who did it although it was not for some reason they knew exactly why they were doing it by the way those software developers are in jail now as they should be so when the event occurs and the politicians are eyes up and say we got to do something about these programmers they're out of control and they point their fingers at us and they say okay how could you have let this happen we'd better have an answer for him because if our answer is you know my boss told me we had to get it done by Tuesday if that is our answer and the politicians of the world will hang their heads in disappointment and shame and they will and disgust and they will do the one thing that we don't ever want them to do they will legislate they will regulate they will tell us what languages we can use and what platforms we have to write on and what courses we have to take and what books we have to read what processes we have to follow and what signatures we have to get and we will all become civil servants I would like to avoid this so how do you avoid it well you get there first you get there first by establishing the ethics of software development what is our ethics do we have a stated set of ethics do we have a set of standards a set of moral standards that all programmers follow do programmers take an oath to uphold a set of standards a set of ethics we don't have that we don't have a profession because of that because in order to have a profession you have to have something you profess and we don't profess anything at this point in time we're going to have to come up with this we're going to have to learn to adopt a set of standards and ethics so that when the politicians of the world do point at us and they will and they say how could you have let this happen we can respond by saying look this was a horrible accent and we regret it but it was not due to our negligence and we can prove it was not our negligence because here are the standards that we enforce here are the morals that we adhere to these are the ethics that we claim to profess and if we can say that to the politicians of the world then when the politicians of the world decide to regulate us they will know how to do it because they will simply take the rules that we've already invented and turned them into law this is what's happened to doctors it's what happened to lawyers it's what happened to architects so it happened to everybody it's going to have to happen to us as well and so you and I have to begin this thought process on what our ethics is what do we value what is it that a software developer holds dear and one of those things had better be the cleanliness of code so let's talk about that now I've got a few things here I'm just gonna quickly go over them here's a fellow his name is Kent Beck has anybody heard of Kent Beck several of you good all right the rest of you should have heard of him by now so do a little bit of research on Kent Beck he's one of the leaders in the field he wrote a book some time ago called implementation patterns that was the name of the book and in that book he said that the book was in the introduction of the book he said that the book was based on a fragile premise and the fragile premise was that good code matters and when I read that in his book I scratched my head and I thought why would Kent Beck have said that that was a fragile premise it seems to me that it's a very rock-solid premise but yes good code matters and it matters for a whole bunch of very powerful reasons so for example why are we so slow why our programmers so slow ooh here has worked on a greenfield project a project where there's no code ah bunch of you how fast can you go those first few days where there's no code and someone comes to you and says can you get a feature done and you think yes you start writing code code pours out of every orifice of your body and you get that feature working and everybody goes whoa you got that working fast it only took you a few days we're programmers can you do it again yes come back to that team a year later can you get a feature working for us hmm tricky probably gonna take us six months he used to be able to do that in a couple of days yeah but you don't know how messy this system has become why if we touch even one line of code all hell could break loose why'd that happen here's the thing that happens to software teams right they start out fast they start out with a beautiful design and they start out lovely in there fast and they write features and everything's working great but they make a mess because they want to go fast they make a mess and as they make a mess as the mess builds the team gets slower and slower and slower until they bottomed out at 1% of their original productivity and there's a but what are you going to do about this let's say you're a manager right and you've got his team this team's been working on this software for two years now and they can't get anything done no feature can get done in less than you know six months and even then it's going to be late and it won't work what do you know is the real world for managers what are you going to do as a man if you've made promises to people you have you've set plans out there there's people expecting features and the teams cannot deliver those features what are you going to do as a manager what would your option be you got to go fast somehow add more people right that's what you do you have to double the staff everyone knows you go twice as fast if you double it and you're laughing why are you laughing because you know this is nonsense you can't go faster by doubling the staff adding more people does not make you go faster what does it do the moment you decide to add new people to a team what happens to that team it slows down why because the new people suck the life out of the old people for months now you're kind of hoping that those new people will get smart after a while and and then productivity will rise but there's another effect that kicks in who's training the new people the people who made the mess in the first place and in fact it's not the old people training the new people it is the old code that trains the new people the new people are thrown into the fire they've got to make some sense out of this system they read the old code they say to themselves oh I see how things are done around here they emulate it of course and just continue to make the prospect problem worse and the code gets Messier and Messier no matter how many people you add to the team and nothing you do can make that productivity rise that's why programmers are slow and slow because they make a mess if they didn't make a mess they'd be fast if you could keep the code clean it wouldn't be a mess you could add new features they would get added in a reasonable amount of time as long as you could continue to keep the code orderly and clean we're going to talk about a number of strategies for doing that but I wanted to impress that point on you pretty thoroughly we go slow because we make messes why do we make the mess what drives us to make the mess in the first place the desire to go fast we make the mess because we think I got to get done quickly they're expecting me to get a lot of stuff done I got it I got to just get it done oh it worked how many of you have done this it's hard to get code to work you struggle to make code work so you're working on the code and you're working on the code and you're trying to get it to work it's not working and you're sitting in the debugger and you're single stepping through it and you're trying to make it work in and then all of a sudden it works Sookie don't anybody breathe move carefully and I'll check it in Co God thank you that's the wrong thing to do the fact that you got it working is only half the job once the code works that's when you have to clean it no one writes clean code first nobody does because it's just too hard to get code to work so once the code works it will be a mess human beings do not think in Nice straight lines they don't think in if statements and while loops they cannot foresee the entire algorithm so we piece the thing together we cobble it together with wire and scotch tape and then it suddenly work so we're not quite sure why and that's the moment when you say all right now I need to clean it how much time do you invest in cleaning it roughly the same amount of time it took you to write it and that's the problem nobody wants to put that effort in because they think they're done when it works you're not done when it works you're done when it's right and if you adopted that attitude well then the code would stay clean and you would never go through the slow down more to say about this later [Music] you have all these slides I never actually used them they tell the whole story but I just kind of wing it anyway dad oh damn boom boom oh here's a good one let me stop there memorize this one the only way to go fast is to go well somebody said today you know twice as fast twice as proud okay fine how do you go fast you go well twice as well twice as proud we might go fast too the only way to go fast is to do a good job if you do a lousy job you're going to go slow donna diva what is clean code alright who knows who this guy is Grady Booch what a great name if your name is Grady Booch everybody knows your name because who wouldn't know that name well that's not granny boots that's yarnís Tristram sorry I picked up back did the wrong side this is your nest rooster who knows who that is he's Danish does that matter I guess not okay so yeah mr. strip and who is he C++ he made the language C++ that's correct so I wrote to yarn I said Jana what does clean code make mean to you and he said and this is this is very typical of Jana stirs drip he said I like my code to be elegant and efficient and then he said this clean code does one thing well one thing well now this one thing idea has been around in software for 40 years or more people are always writing about how a function should do one thing and one thing well it's a very very old idea and strip echos it here but what does one thing mean it seems to be a kind of subjective subjective measure what does it mean for a function to do one thing well I think I know the answer to this and I'll tell you a little bit later I think I have a completely objective way to measure one thing and if you if you adhere to that objective way it transforms the structure of your code remarkably there's Grady Booch it was in there somewhere Grady Booch the chief scientist at rationale he wrote a book in 1988 called object-oriented software design with applications anybody read that book 1980s late eighties do we have any baby who was born then yeah okay good all right so that's fine that fascinating book very early book on object-oriented design Grady Booch is also the first person I believe to have the title chief scientist I think he invented that and rational said yeah you can be the chief scientist that's fine and ever since then everybody's wanted to be a chief scientist at some company somewhere so I asked Grady you know Grady what's clean code he said clean code is simple and direct fine and then he said this clean code reads like well-written prose have you ever read code that read like well-written prose what does that mean well written prose now I think I know what that means and I think I can show you what that means as we go along I think I can tell you what code that reads like well written prose means and let's go to Michael feathers Michael feathers I wrote to Michael I said hey Michael what's clean code and he said clean code always looks like it was written by someone who cares what a lovely statement that's a good attitude right there clean code always looks like it was written by someone who cares when's the last time you read a module and your thought as you are reading module was the author cared about me the author cared about everybody else who is going to be reading that code when's the last time you had that experience the author of this code cared about me very interesting and by the way it brings up a fascinating point what's your job you may think that your job is to get code to work that's not your job that's only half of your job and it's the least important half of your job the more important part of your job is that you must write code that other people can maintain and use and make work if you hand me code that works perfectly but I can't understand it then as soon as the requirements change that code is useless on the other hand if you give me code that does not work but I can understand it I can make it work it is much more important that your peers be able to understand the code you write then that the computer can understand the code that you wrote it is more important to communicate with your peers using a programming language than it is to communicate with the computer because if you do that well somebody will make it work the last one word Cunningham who knows who worked Cunningham is somebody heard the name you know what that isn't few of you do I said know you'll know who he is as soon as I tell you he's the guy who invented the wiki who's he's the wiki everybody puts their hand up ok good Ward Cunningham is the guy who invented the wiki he invented the wiki out of 19 lines of Perl in 1990 something or other put it up on the on the website by the way that very first wiki is still alive you can get to it if you want to the URL is C to calm the letter C and the digit to calm is the very first wiki ever it's still there and by the way it's full of fascinating stuff you'll see all kinds of design pattern stuff and extreme programming stuff and agile stuff because it was there at the beginning and I asked Ward Ward what's clean code and he said this you know you're working on clean code when each routine you read turns out to be pretty much what you expected when's the last time you read code and as you're reading it it was pretty much what you expected you reading along and you're going yeah yes yep yep yep yes mmhmm yep yep when's the last time you had that experience what he's saying is no WTF s per minute zero clean code is no surprises no WTF everything is pretty much what you expected that's good clean code and that's what we're gonna pursue over the next few hours now I want to go to a different part of this presentation let me just cycle up here now I've been preaching for a while now I think we've got a little bit of time left I think I would go till 10:45 if I remember correctly so we've got enough time for this that's good I am going to put some code on the screen it'll be three pages of code I will give you one minute per page the last page is half a page so you'll get two and a half minutes the code is Java if you're a c-sharp programmer you won't be able to tell the difference because they're the same language right read the code figure out what it does and then when we're done I'll ask you what it does and we will begin now what that could do what said a good it generates HTML and you knew that because the very last line was get HTML good what was the name of the function testable HTML good so we got the first line in the last line what the middle do so some of you may have gotten the idea let me let me just walk you through it I'm not going to walk you through the whole thing I'll just tell you what it does this is a little bit of code in a in a tool called Fitness fitness is a wiki some of you may have noticed that it was a wiki Fitness is also a testing tool it allows customers and QA people to define acceptance tests in the form of pages now if you are used to a testing environment you know that tests typically have setups and tear downs in this tool those setups and tear downs are on different pages so the job of this code is to take every test page and then find all of the setups that are appropriate and prepend them and find all the tear downs that are appropriate and append them and then take the whole thing and generate HTML and feed it into the testing engine that's what this is supposed to do so this function up ends setups and tear downs to a test page what was the name of the function testable HTML terrible name for a function by the way that's a noun you don't want nouns as function names function name should be verbs because functions do things now let's let's look at this function a little bit more there's quite a few bad things going on in here when we read a little bit here let's see we've got this nice thing right here that first line wiki page and if you're a programmer in this environment you see that and you kind of heave a sigh of relief because the wiki page is the highest level abstraction in this system it gives you a great comfort to know that you can recognize that first line the next line creates a string buffer so now we are going from the highest level concept in the system to one of the lowest level things in a Java program this is rude the programmer is being rude the programmer is taking you from the heights to the depths in the span of one line there is a fundamental rule for a function and the rule is that every line of a function should be at the same level of abstraction and that level should be one below the name what's happening here well look I mean heck he goes to the wiki page first and then to the string buffer so up and down and then he goes to a slightly high level thing that's the page attribute and then he's got an if statement another wiki page that's nice and high level page crawler that looks like it must be high level ooh there's a null check that's pretty low level isn't it you keep on reading down and you get to hear a dot is that dot important does that dot have to be there you're the programmer trying to understand this code what does the meaning of that dot we've gone from the highest level concepts to adopt this is route now why is the code written this way well the code is written this way because this is how you write code when you are writing code your brain does this oscillation from high to low level and it works like this you sit there and you're writing the code you think all right I'm gonna need a wiki page all right get the wiki page okay I'm gonna need a string buffer ok string buffer okay I better check something all right if statement oh it might be null check for now okay this is the way your brain works right as you're writing the code so as you're writing the code you are of course creating this code that goes up and down the abstraction levels which is rude not to you the author but to the reader the mistake that the author here made is that the author got all this working and then didn't fix it so let's continue we've got all this up and down stuff and you can kind of see that obviously I want you to focus though on this null check which is followed by a page crawler which is followed by three appends null check page crawler three appends oh look now check page crawler three appends now check page crawler four appends what's the extra pen who sent line in is that line end important that line end has to be there no check page crawler three appends this is very clear what the programmer did here the programmer got the first quarter of this working and then like any good programmer did a copy-paste and he fiddled that part into working copy paste he fiddled that into working copy paste he fiddled that into working perfectly normal way for a programmer to behave when they're trying to get it to work he just didn't go back and fix it he left it in this intermediate working state now by the way the offer very well could have been me it's not unlikely that I wrote this code although it's possible someone else did too so I'm not claiming authorship of it but I do claim that many years later I saw this code in fitness and thought analysis ugly I should fix it so I started to refactor it let me show you the an intermediate refactoring this is not the final refactoring it is just a refactoring that all was about halfway through I'll give you about ten seconds to look this over what's that do first of all did anybody notice that the original function was completely surrounded by this if statement it was but it was kind of buried very hard to see in that original code here you can kind of see mmediately it's all about this if statement so most of this code doesn't get executed unless this is a test page take a look at that if statement the if statement fascinating because it uses a variable the variable is called is test page now is test page is defined right above it this is called an explanatory variable the only purpose for that variable is to explain what its contents is and the contents is what you would have put in the if statement page data that has attribute colon test well I think it reads a lot better to say if is test page this is one of the ways you get code to read like well-written prose you construct well-written prose from the names of variables and functions now if you read further we get the wiki page fine and we get the string buffer so we're still going up and down the abstraction hierarchy a little bit and that's that's still bad but okay after that we include the setup pages we append the content we include the teardown pages we set the content and convert it all to HTML it's not very hard to understand what this code is doing still some problems with it it's got a much better name render page with setups and tear downs that's better maybe it's not perfect maybe it should be rendered test page with set ups and tear downs but okay looks like a pretty good name reasonable structure things are getting better here why is this better what makes it better why is it easier to understand it's smaller that's the reason you don't need any other reason beside that it's smaller and if smaller is better well let's turn that knob up to 10 let's make it really small here let me show you where it finally ended up that's the final refactoring of this function render page was set up some tear downs if it's a test page include the set ups and tear downs converted to HTML takes you know time to understand this function this function is polite why is it polite what do I mean by polite so there's anybody studied journalism here you know how to write a paper the rules for writing an article or writing a paper are very very simple you start with the title the headline the title right then you have a paragraph usually called the synopsis or the abstract it's usually one paragraph and it describes everything in the in the paper in high-level terms and then the next paragraph down is slightly more detailed the paragraph after that is a little more detailed than that and as you read downwards the detail increases in to get to the bottom where there's all the names and dates and guilty parties and everything like that this is polite it's polite because of what it allows the reader to do it allows the reader to escape early what is your algorithm for reading the news given a webpage up with the news how do you read it or you scan it for a headline that you think is interesting okay if that headlines interesting I'll read the first paragraph you read the first paragraph if it's still interesting you read the second paragraph if it's still interesting you read the third paragraph if it's still interesting you read the fourth paragraph notice the while loop here and you exit that while loop as soon as you get bored that's how you read everything in the news nobody ever reads the whole article you just read until you're bored and then you get out this is polite it is polite to allow the reader to exit early and this allows you to exit early if you or some guy and you saw a call to that function render page we'll set up some paradigms and you said gee I wonder what that function does and then you went here within three seconds you know what this function does at a very high level not a level but maybe you didn't want to know it at a detailed level maybe you just wanted to know oh yeah okay if the test paid you include sit-ups and turnouts okay and you get out early there was no way to get out early from this code the only way to get out of this code at all is to understand it all completely including all the dots and it would have taken you thirty minutes thirty minutes you would have poring over this code wondering what the devil is this guy doing why is he doing it this way what's good and at the end of that thirty minutes you would have finally gone oh if the test page he's including the setups and tear downs why the hell didn't he say that how did I get this code shrunk down to that last little bit how did that process work my goal was to make these functions small and I call this the first rule of functions the first rule of functions first rule is that they should be small the second rule is they should be smaller than that I want to turn the knob up on this really high I want the function small really small how small should have function be let's see what's the proper size for a function how many lines should it be one for three sit on your screen that was the old rule by the way back in the back in the 80s when we first got screens does anybody remember when we first got screens but there was a time we didn't have screens we wrote our code on paper in the early days of programming programmers did not know how to type we had no keyboard skills we wrote the code in pencil and we had other people enter it into punch cards for us but then eventually we got screens and we started typing ourselves that was in the 80s and those screens a typical screen was 24 lines by 72 columns why 72 columns yes part holes on the punch card there were 80 columns on a punch card the last eight were sequence numbers so we only needed 72 on the screen that's the reason they were 72 you didn't even know they were 72 did you well now you know and the rule came about your function should fit on a screen well that meant that the functions had to be about 20 lines of code is that the right size I have a better rule a function should do one thing a function should do one thing that's the rule for how big a function should be it should do one thing but now we need to define what one thing is what's one thing what idea are you using i hear people going IntelliJ IntelliJ who's using IntelliJ oh yeah tell Jay it's the best idea it really is the best idea out there there's just nothing better is anybody using anything else if you are I'm sorry what is it eclipse and well VI you know everybody has to use VI from time to time cuz you've got to edit some text file and there's just no easier way to go bij jkkk it's fine right fine but if you're if you're editing code you don't want to use VI for that cuz that's a pain so you use something like IntelliJ that's nice okay IntelliJ it's got a refactoring menu one of the menu items in there is called extract method who's used extract method we can add everybody use extract method that's good okay so now you know how extract method works I'm going to define one thing a function does one thing if you cannot meaningfully extract another function from it if a function contains code and you can extract another function from it then very clearly that original function did more than one thing because you could extract something from it so I want all my functions to do one thing and that means I must extract and extract and extract and extract until I cannot extract any more I'm going to take all the functions in the system and explode them down into a tree of tiny little functions optimally extracted maximally extracted at this point there are people in the room going this guy's nuts he's insane I'm not going to do that if I did that I'd have thousands of little tiny functions I would drown in a sea of tiny little functions no you will not drown in a sea of tiny little functions and there's a simple reason why you're not going to drown in a sea of little functions and that's you're going to have to give those functions names you'll have to name those functions and as you name them you'll have to move them into appropriately named classes and appropriately named packages and appropriately named source files and modules and you will create a tree a semantic tree of functions that you can follow by name now you may not believe me but let me make a few points I'm going to draw for you a function that I wrote in 1988 probably the name of this function was gi gi stood for graphic interpreter it was 3,000 lines long I'm going to draw it for you not all the code just the shape of the code you recognize that don't you and that was the shape of the code well it was actually more complicated than that but look at that shape and see if you can tell if there's some part of your brain that relaxes because you see that shape there's some part of your brain that could oh why why does that happen because beep when people get very used to a large function or a large module you've been working in it for months you know it you know it really well you know it geographically you know it by its landmarks you know the shape intimately and look at that shape rotate that shape 90 degrees it looks like the horizon humans evolved to know where they are on the planet by staring at the horizon they know over there by those Peaks that's where the watering hole is and the saber-tooth wanders over there so you look at that shape and some your brain goes yeah that looks like home now this was written in C by the way if someone had come to me in 1988 and said you know Bob this 3000 line function does a lot more than one thing I would have said no it can't it interprets graphics because the whole notion of one thing was so horribly subjective at the time but now I know how to make it objective extract extract extract until you cannot extract anymore now let's assume that this function written in C has some variables where were this where were the variables in C the local variables of a C function where did you put them at the top that's right C programmers in the room know right you still have your copies of Kern and Richie sitting on the Shelf don't you can't be far away from it so okay let's say that there's a couple of variables here int I and J good now let's say that this indent right here manipulates I and J and it does this it says I equals 0 and J equals 2 okay semicolon good now you want to practice extract till you drop do you want to do what I've just told you to do extract extract extract extract so you highlight that highlight that indent with your mouse and you invoke the extract method function of the IDE and the IDE will come back with an error message and say I can't extract it because it changes two variables and I can't extract code that changes two variables well what are you going to do now you want to extract it but you can't because it changes two local variables what are you gonna do now make them global right that works perfectly you think I'm joking don't you haha but now look you can extract that and you can extract this one into another function so now I've got two functions I've extracted them out I can take that one and extract it yeah I can take that one and extract it and I've got something very interesting here now I have a set of functions all of which manipulate a set of variables what's it called when you have a set of functions that manipulate a set of variables that's called the class there was a class hiding inside this big function and if you think about it of course there are classes that hide inside big functions because big functions have a whole bunch of variables and a whole bunch of indents that manipulate those variables so of course every large function is really a class with a bunch of little tiny functions inside it and if you start extracting and extracting and extracting you will begin to identify these classes that you would otherwise not have identified and you'll be able to put them in appropriate names and spaces and allocate them nicely and partition your code well this is what happens when you start to extract and extract and extract you find the true object-oriented structure of the system that you're trying to design we're all object-oriented designers we all use object-oriented languages what language are you using well you're doing intelligent must be doing Java right everybody doing Java who's doing Java Oh who invented Java and when and why his name was James Gosling in the year was 92 or 93 why did he invent this language Oh someone said it good good okay yes he was he worked at Sun Microsystems in the contract programming division and they got a a contract to write the code for a cable television set-top box now son was dedicated to C++ at the time so he was supposed to write this in C++ but he hated plus plus anybody here hate C++ okay fine well now you know why right so he hated C++ and decided he would write his own language which he called oke Oh a K oke and lovely fine he got it all to work and life was good and then the contract and didn't the language went in the garbage bin where it belonged that would have been the end of it except for an accident of history the accident of history is very interesting because Sun Microsystems was a hardware company they sold pieces of metal they sold chunks of hardware and their whole marketing scheme was about selling hardware and they realized in the early 90s that the best way to sell hardware was to win the hearts and minds of programmers first time that had been realized that programmers are the ones who make the buying decisions prior to that paper trying to sell the CIOs and CTOs and CEOs but when they realized that no no no it's actually programmers who make these buying decisions because they influence the executives never underestimate your power you're the ones who know and so son says how are we going to win the hearts and minds of programmers what better way than to give them the language of the Internet and so they looked around on what language should we use and here's Gosling over in the corner and he reaches into the garbage can and he takes this oak thing out and he says you could use this one I think executives in the market ears I'll say I have fine that's fine if I don't like the name it should have some better name something stimulating like coffee dalla and they won the hearts and minds of the programmers you'd like to think that Java was created out of some bursts of creative energy but it was foisted upon the programming community as a marketing tool to win your hearts and minds it was a manipulative event keep that in mind where did c-sharp come from Java it is Java Microsoft just took it does anybody remember visual j+ + right make yourself to him and sun microsystems said hey you can't do that and microsoft said oh ok we'll change the : ah how much indenting do you think you would do if you extract and extract and extract how deep will your indenting be if you extract and extract an extract one or two yeah one or two is about it usually one well actually usually none right just open brace 1 indent couple of lines of code close your functions will really be about four lines long 3 4 or 5 lines long something like that every once in a while you'll get a 6 liner switch statements tend to get longer you don't like switch statements so you don't have too many of those I hope because they're evil switch statements bad things to have around really the same true with if-else statements we don't want those either so we tend to give these little tiny functions now think of what happens to normal code take an if statement if you are extracting and extracting and extracting what is the body of the if statement it's a function call yes and it has a nice name a name that tells you what the function is going to do so you say if something then do this it reads like well-written prose what's in the parenthesis of the if statement a function call with a nice name that tells you what you're testing if employee is too old fire employee it works perfectly right it reads like well-written prose how many arguments should a function have well zeros a good number right cuz it's really easy to understand a function that takes zero arguments but you don't have to worry about any if statements in there that checking the arguments for anything there's no arguments one is not too hard to understand one argument going into a function is pretty easy that's you know mathematical f of X we kind of get that two arguments going into a function yeah it's okay you know the human brain is pretty good at keeping two things in order there's only two different ways to order them so not too hard three arguments it's a little hard how many ways are there to order three arguments six yes it's n factorial so ooh six is hard now humans can probably do that sort of what about four how many ways are there to order four arguments twenty-four twenty-four different orderings how about five one hundred and twenty ways is n factorial big crimes enormous ly fast so probably don't want any more than about three arguments in a function that's the way I like to limit it I don't like to have functions that take more than three arguments and by the way there's another there's another debate here I almost use the word argument um if you have a function and you want to pass six things into it those six things are so cohesive that they can be passed into a function together why aren't they already an object this is an interesting debate to have here you probably never need to pass more than three things into a function so I I like to use that as a a soft rule I don't want to see a long comma separated list of arguments that seems to me to be rude I would like it to be polite so keep the number of arguments down to two or three create objects if you have to use other strategies to to get things into functions by creating objects and data structures things like that what types of arguments should you never pass into a function boolean's boolean's now by the way I use the word never never is the wrong word mostly never is probably a better way to put that don't pass boolean z' into functions why not well because if you pass a boolean into a function there must be an if statement in that function and that if statement has two branches the normal branch and the else branch why not just separate them into two functions call the one in the true case call the other in the false case have you ever read code that has boolean arguments it's rude now do this comma 5 comma 6 comma true what does the true mean I don't know it must be true though and here's how you read this code when you're reading this code you stare at that boolean and go oh wow that the author probably knew what he was talking about and you walk away you're gonna go read what the boolean does is probably some stupid if statement in the middle of the function don't pass boolean surround they're just annoying now that can't be a hard and fast rule because there are times when you want to pass a boolean around for example you are setting the state of a switch you know sets which bool ok fine but don't use it as a little testing argument into functions that's just rude it's annoying another thing that's rude is output arguments arguments that are passed into a function for the purpose of collecting the output nobody understands that right you're reading along and you've probably all had this experience where you're reading along and you read this line and there's an argument at the end of the function call and you're not quite sure why it's there it seems out out of context it's just a bizarre argument but you've got this vertical momentum as you're reading who's had this experience right you're reading down and there's something about this line that puzzles you but you've got this nice vertical momentum so you keep reading but a little process is started in your brain and this little process starts yelling at you louder and louder you didn't understand that last line you didn't understand that lining your eyes are torn back up to look at that line this process in your head takes your takes your head and moves it back to stare at that line this is a double take you know a double take it's I think it's American slang double take a double take is like this you're out on the road your start on the sidewalk you're walking down the street out of the corner of your eye you see an attractive individual you turn away and then a little process in your brain goes wait that was interesting and you go back that's a double take that code that makes you do a double take is rude it's rude code it forces you to stop your reading and go back so you don't want to have these double take moments in the code there's another author who says this is the principle of least surprise make sure that your code is not surprising do one thing yes I did that did that one yes yes that's all the abstraction at the same level yes extract to you drop did that good avoid switch statements why what's wrong with switch statements what's that they break why do they break oh but you might forget them yes okay good so switch statements what goes wrong with switch statements what do they do more than one thing that's true so let's say that we've got a switch statement the switch statement switches on oh the type of a shape so there's a shape and it's there's an enum somewhere that I define circle and square and triangle and so on traditional kind of kind of objects and you've got a switch statement that switches on this shape type and in fact how many such switch statements will there be in the system because your system deals with shapes how many such switch statements will there be well you're going to have to have a switch statement you draw a shape you'll have to have another one when you rotate a shape and another one when you erases shape and another one when you drag a shape another one when you stretch a shape in fact every time you do anything to a shape you'll have to have a switch statement now what goes wrong you add a new type of shape what happens when you add any type of shape you've got to find all the switch statements you've got to go through the whole code you've got to find all the switch statements are you going to find them all are they all switch statements they might some of them might be if-else statements and then there's this problem rotate shape what do you do in the circle case nothing there's no case for the circle so the programmer does some nice logical optimizations here's the problem now right you've got to add a new type of shape rhombus and you've got to find every switch statement in the system and you've got to investigate every switch statement in the system logically decoding them to make sure you put the rhombus part in in just the right place and this is fragile this breaks it's hard to do it causes lots of difficulties what's the solution polymorphism is the solution of course we don't want to have a switch statement we want to have a base class called shape and we want to have subclasses for triangle and circle and square and rectangle and all of these interesting derivatives and then we can put all of those functions into the derivatives we can put the draw function and the rotate function and the drag function and the square file all of those functions can go into the derivatives and now what happens when we add a new shape what changes in the system when we add a new shape we have to add a new file new class new subclass yes but nothing else in the system changes there are no such statements the switch statements are all gone nothing else in the system changes this is called the open closed principle the open closed principle says that a system a module should be open for extension but closed for modification you should be able to extend the behavior of a module without modifying that module and how do you do that well you do that by creating base classes and having derivatives our system can now be extended with new shapes without modifying anything in the system we have to add something to the system we don't have to modify anything this is one of the reasons we don't like switch statements but just one there are other reasons we don't like switch statements we don't like switch statements and I better draw this one [Music] doo-doo-doo-doo here's a switch statement with a bunch of cases it's in a module each of these cases does something but let's say in this particular case these cases call out to other modules look at the dependency structure here we've got a single module that throws a whole bunch of dependencies out to other modules these are source code dependencies the switch statement must import all of these called modules so the import statement is a long import statement there's a source code dependency going from the switch statement to every one of these outgoing modules now we've got other modules in the system that depend on the switch statement if I make a change there what has to recompile everything everything has to recompile what has to redeploy everything everything to the left the switch statement has to be redeployed and everything to the left of the switch statement has to be redeployed because it's all getting a recompiled switch statements act as a dependency manager manic magnet a dependency magnet they throw out a big net of dependencies that cause it to be difficult to independently deploy modules do you independently deploy do you do you a move your system into jar files do you partition your system into jar files what is a jar file yeah it says Java archive that's what jar stands for fine thank you but what is the intent of a jar file what is the equivalent in dotnet a DLL what this DLL stands for dynamically linked library what does it mean to be dynamically linked first of all what does it mean to be linked see programmers know what does it mean to be dynamically linked everything gets loaded at runtime all the external variables get linked at runtime that's what a jar file is it's a runtime linking loader does anybody remember the 80s when we would execute absolute binaries who was the C programmer in the 80s oh yeah some guys here C programmers in the 80s right again how did you do this right you would compile dot C files into dot o files that were object files and you collect all your files and then you'd link all without o files together into a dot XE and then you could execute the XE and by the way the longest-running effort there was the link the link took forever and why did the link take forever because disks were slow and we didn't have a lot of memory in those days but as we got into the 90s that really got faster the disks got smaller and faster and really tiny and much more reliable and link time started to shrink like crazy and Microsoft was one of the first ones to say hey we could use that to dynamically link so they created ActiveX anybody remember ActiveX horrible decom stuff okay and then along comes Java and we've got jar files and we've got DLLs that life is good so a jar file is there so that you can independently deploy chunks of your system now what would you like to independently deploy so you don't have to deploy everything what would you like to independently deploy why what would you like to deploy separately well now let's think about this yes modules is the right answer but which modules what modules would you like to deploy separately from which other modules which parts of the system changed capriciously change for stupid reasons the business requirements change for stupid well they're not stupid reasons right they change but it's not for stupid reasons the stuff that's changes for stupid reasons is the GUI there are people that just say you know I don't like the color that color should be a different color I don't like to say I don't like the shape of that thing that should be around and let's take that page and move stuff around on it has nothing to do with the business rules at all has something to do with some marketing guys idea of what would look better on the screen how many of you have faced the problem that when there's a change to the GUI it breaks a whole bunch of business rules you don't want that to happen you want to isolate the GUI from the business rules we're going to talk about that tomorrow and we talked about clean architecture and so what we'd like to be able to do of course is independently deploy the GUI from the business rules independently deploy the database from the business rules so that if there's a change made to the GUI we can redeploy the GUI without redeploying the rest of the system and we can do that if we are very careful not to throw switch statements all over inside the systems that was why we don't like switch statements there's a letter from my wife okay I'm gonna read this there is no water in the building because a pipe broke in the street this problem might be resolved before 11 o'clock how are your bladders you can continue until 11:00 I see we're not going to stop at 10:45 I get it they're trying to tell me this so I actually didn't have to read this to you if there is still no water at 11 o'clock we'll be doing an announcement before that so okay fine all right we understand thank you thank you got it all right 11 o'clock now all right I'm going to talk about names a little bit later I've talked about arguments already good and flag arguments and output arguments no side effects what's a side effect so the classical definition of a side effect is a change to the state of the system if you call a function and that function causes the system to change state then that function had a side effect the function open has a side effect because it leaves a file open the function new has a side effect because it leaves a block of memory allocated side effect functions change the state of the system side effect functions come in pairs there's open and closed new and free are new and delete in C++ and Java we fixed that problem semaphores season release side effect functions come in pairs they're like the SIF always to there now how good at we at managing pairs of functions like this for example how good are we at managing Alec and free the answer to that is that we're terrible at managing that and the the obvious evidence of our terrible ability to manage pairs of functions is that in modern languages we've invented a horrible hack to allow us to forget about managing pairs of functions that horrible hack is called garbage collection now I would not want to program without garbage collection because garbage collection makes it much easier to write safe code but you must admit that garbage collection is a crutch it is not reasoned you did not write the code in a reasoned way you did not free everything you allocated instead what you did is said the system will take care of it and ok fine we have we have written this horrible hack we've we've declared that we're going to depend upon it we've acknowledged that we need the crutch but allocate allocation and freeing is not the only side effect function there are many other side effect functions that you and I have to deal with like open and close does anybody seen a system crash because too many people forgot to close files yes and you leave a bunch of file descriptors open in the operating system and eventually you run out of file descriptors that's called a file descriptor leak has anybody seen a system crash because all the graphics contexts got leaked or the semaphores didn't get closed anything that comes in a pair like that will suffer the same fate that memory used to suffer when we had memory leaks and by the way you can still have memory leaks in Java you just have to have to work really hard at it so what do we do about this what do we do about this problem of of controlling pairs of functions pairs of functions must be called in the right order you cannot close a file before you open it you cannot free memory before you allocate it if you call them in the wrong order it's a logical inconsistency how many of you have debug based system spent days and days debugging a system only to find that you can make it work if you change the order of two function calls and you don't know why but somewhere in there there's some side-effect and if you just change the order oh that makes everything work what can we do to manage that so up what version of Java are you using you're working on lambdas now Java but what is that eight Java eight everybody doing Java eight everybody familiar with lambdas now you know how to do lambdas and you can pass lambdas here and there and everywhere good I don't know why they put that feature in the language so what can you do about this well if you've got lambdas in the language it makes things a lot easier well it makes things a little bit easier remember that the lambda is just a class and it's a class with one function in it called execute you could have written that yourself but they decided to put it in the language so okay fine let's say that we want to make open safe and I think in the Java library now they actually do this so okay here's our open function our open function is going to be a void it doesn't return anything and it's going to take a filename so that's a string that would be the file that we're going to open and then we're going to pass into it a lambda and this will be we'll call this lambda process of course I'm not using Java syntax but you get the point okay there's the open brace now what do we do well first thing we're going to want to do is we're going to really open that file so we're going to call the low-level open function so here we say file F equals file dot open of FN good so now we've got the open file the next thing we do is we say process that file so now we're calling the lambda and now we say file dot close 1/2 and return this is a simple function that deals with the side effect this function does not have a side effect because it leaves the system with the file closed so the side effect is dealt with inside of this function you don't have to remember to close it what you do have to remember to do is pass in the lambda that processes the open file this is a very common procedure for dealing with side effects so you can try to get your side effects under as much control as possible by passing a lambda into your system if you don't have lambdas in your language then you could use a command object a simple a simple class that has one function in it called execute and then you pass in the appropriate derivative data side effects doop-doop do yep good command query separation a function that returns void must have a side-effect if it doesn't have a side-effect there's no point in calling it so a function that returns a value should not have a side-effect this is a convention that we like to follow called command and query separation commands change the state of the system therefore they return void anything that returns of value by convention will not change the state of the system and that way when you see a function that returns a value you know it's safe to call it it will leave the system in the same state it was found in this is a convention that I like to follow the language doesn't enforce it of course but I like to follow it because it allows me to keep track of side-effects to prefer exceptions to returning error codes do I even need to go over this dude use since exceptions a lot in Java everybody using exceptions good good good does anybody remember how awful exceptions were in C++ okay so we didn't use them I don't use them in C++ and Java they're fairly safe it is better to use an exception than to return an error code I'm not going to belabor that point but I will make another point when I write a try block the only thing in that function that has the try block is the try block I don't want to have a lot of code before the try block if I've got a function that throws an exception the first executable statement in that function is going to be try and then there will be a single function in the try block that's the function that actually throws the exception and then there will be a closed brace and then the catch blocks and a finally block if necessary and then no other code in the function I don't want anything in the function except the try block I don't want a whole bunch of code in the try block I want that to be a different function I don't want any prefix code in that function I don't want any suffix code in that function just the try block because error processing is one thing so I want the I want the try block completely contained by a function and I never ever ever want nested track patch blocks I will find you if you do that [Music] there's a rule in software called the DRI principle don't repeat yourself this has to do with duplicate code you saw some duplicate code in that original code that I threw up on the screen a little bit earlier that code was obviously copy and pasted we'd like to avoid duplication as much as possible because it's sloppy if you do you copy and paste a bunch of code it's just sloppy to leave it in that state what you'd like to do is move the copied code into some function and call of a function of course sometimes you copy the code and then change the code you've copied and so that means you're probably going to have to put it into a function that has some arguments but that's all fairly easy to do so we don't like duplicated code we don't like code that's kind of duplicated we ought to be able to move those into functions but what do you do when it's not the code that's duplicated it is the loops that are duplicated how many of you have seen this problem where you've got a complex configuration data structure to walk this complex configuration data structure you have to have a big nested bunch of loops a bunch of while loops and if statements that allow you to walk through the Kombi the complex configuration data structure and then you finally get to the end nodes in there and you've got a bunch of processing code that processes the end nodes and then you see that same loop repeated over and over and over again inside different parts of the system as the different parts of the system walk different parts of the configuration database how can you get rid of that duplication one of the answers to that as well if you've got lambdas you can put that nice looping structure into a function that takes a lambda argument and then you pass the processing code into the lambda argument so you can get all of those duplicated loops down into one and then just pass a lambda in or pass an object that takes a a single single parameter which is a function we got about 10 minutes I'm gonna lighten them lighten the mood a little bit structured programming what is it what is this thing called structured programming when was it invented who invented it why Michael Jackson no actually although he did a lot of a lot of books on structured programming it was invented by Edsger Dijkstra here in the Netherlands Edgar Dijkstra was the the first programmer of in the Netherlands one of the first programmers in the world but the very first programmer in the Netherlands he survived the Nazi occupation of during World War two he came out of that and and went into school he wanted to become a nuclear physicist he saw computer the very first computer in the Netherlands and fell in love with it he wanted to study software but he went to his his advisor and said I there's no body of knowledge here there are no disciplines there's no formalism I don't think my peers will take me seriously if I study computers and his advisor said well Metzger maybe you will be one of the people who will invent those formalisms and disciplines and add to the body of knowledge and Edsger Dijkstra took that as a challenge and became the Netherlands first programmer he went on to study software in those very early days in the 1950s interesting sidenote he got married I don't remember the date but it was in the late 40s or early 50s that he got married and he had to put his occupation on his marriage license and he put programmer and the officials wouldn't accept it because that wasn't a known profession so he changed it to nuclear physicist he said he made the more difficult choice programming was more difficult than nuclear physics in 1968 Dijkstra wrote a letter to the editors of one of the famous magazines at the time and he said that go-to was considered harmful very famous note and it it kind of caused an uproar in the tendons in the software community because it during those days go to was how we got things done we used to go to for everything we had if statements that would have go to Xin them we didn't have languages that had while loops in them we would just use go twos all over the place anybody here remember Fortran anybody for to add weights before trying programmers in the room yeah since go two's for everything and so Dykstra comes along and says yeah go to Zura problem and the world kind of went nuts for about five years now we didn't have a face book in those days you couldn't flame anybody right so what you did instead is you wrote letters to the editor of the trade journals and people wrote the most scathing letters to the editor Dijkstra's an idiot because of this and other people would say no Dijkstra's a god because of this and these letters went back and forth and it all settled out do you have a go to in your language no you don't do you and no modern language has a go to some modern languages reserve the word did you know in Java that go-to is a reserved word specifically so that it cannot be implemented right Dijkstra won that battle he won it by all the languages beginning to adopt the the structure now why did Dijkstra not want DotA's what what was harmful about go twos so Dicer was an interesting fella he wanted to turn software into mathematics he wanted to create a set of postulates and then a set of theorems like Euclidian geometry he wanted to construct theorems of software his his vision was that you and I would write applications by adopting well proven theorems and then writing little lemmas to adapt them that was his idea there would be this vast library of fear proven software and so he began to work through the mechanics of how you prove software correct and and the mechanics were fascinating what he discovered was that you could write a simple proof for any two sequential lines you could write a slightly more complicated proof for an if statement to prove a loop correct you had to use induction so that was a little more complicated but bit by bit he was able to build up a simple structure of mathematical proof but then he noticed something there were certain algorithms that could not be proven correct there was no rational way to prove them correct and he discovered that those algorithms were were those that had unrestrained go twos this is something that actually touring had proved in 1936 it's the halting problem it goes back to the halting problem of 1936 which is that there are certain algorithms that cannot be proven in that cannot be proven correct the reason they cannot be proven correct is because they have unrestrained go twos he fell back on another theorem that two other guys had written about the same time which was that every algorithm can be composed of three structures sequence selection if-then-else and and iteration loops every algorithm can be written out of those three structures so Dijkstra said okay no go deuce everybody has to use these three structures that will guarantee that the algorithms can be proven correct we never bothered to prove anything correct Dijkstra's whole vision failed we don't prove our software correct we fell back on something else Dijkstra's vision was this mathematical superstructure like Euclidian geometry we do not have that Dijkstra's vision failed but we do have something else there is a branch of knowledge that you and I risk our lives on every day our lives depend on this branch of knowledge every day it cannot be proved incorrect and yet we very happily risk our lives with it every day this branch of knowledge is called science science is a set of conjectures and hypotheses that cannot be proven correct experiments can prove them false but never true you and I risk our lives every day on things that are not proven correct we have not proven that airplanes can fly right the science is not proven correct it has simply been surrounded with so many tests that there's no point in saying that it's not correct any more software could be proven correct but we abandon that we gave up on it it's too hard but we can test it we can use science and we can write tests that demonstrate that the software is not failing we don't know if it's correct but it's not failing we treat software like a science not like a mathematics this was Dykstra's failure Dijkstra thought we were headed headed towards the mathematics or not we're headed towards of science and we prove our software not incorrect I'm sorry for the double negative that's the only way to say that we don't prove our software correct we demonstrate that it is not incorrect by surrounding it with tests how many of you write tests ok that's not all of you so then I have to ask what the hell is the matter with the rest of you okay so how many of you write tests for every line of code that you write mmm that's a much smaller number isn't it why would that be why would you not test every line you wrote what would motivate you to bypass testing lines that you wrote and I'm gonna write these lines I'm not gonna test them why would you do that if they answer that question is part of the ethics issue here now right why would you write code and then not test it now you might say ok well I'm testing the whole system yes but are you testing the individual lines that you wrote we'll talk about that later but I think it's 11 o'clock and it's the water working

Channel: UnityCoin

Views: 1,150,626

Keywords: programming, software, clean code, polite code, shrunk code, programming language, computing, technology, society, ethics, human relations, uncle bob, robert cecil martin, edsger dijkstra, grady booch, future, rules, java, c#, c++, microsoft, functions, declarations, arguments, cycle, kotlin, InteliJ, methodology, agile, scrum, tdd, test driven development, programmer, responsibility, expectations, architecture, design, development, applications, app, structure, web, study, practice, optimization, productivity, purpose

Id: 7EmboKQH8lM

Length: 108min 42sec (6522 seconds)

Published: Fri Aug 09 2019