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What does reasoning about code even mean?

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Programmers talk about “reasoning about code” all the time, but what does that actually mean? Is it really just pretending to be a CPU and working out exactly when your for loop ends?

Yes and no. Figuring out exactly what your loops are up to is part of it, but at a higher level it’s also about how your methods, objects, modules, functions all work together. Like this stackoverflow answer says, writing code isn’t just about cranking out something that compiles, you’ve also got to be able to figure out if it’s actually right, if it performs well enough, if it can be scaled, if it’s vulnerable to bad data (whether that’s malicious or accidental).

Sadly, tools can only help you so much with everything that comes after getting your code to compile. The compiler can tell you whether your code will run, but it can’t tell you if it does what you meant. Automated tests are a huge help with that, but those tests are code themselves and you also need to be able to reason about them to make sure you’re testing what you meant to test and that the test itself isn’t broken.

To figure out what your code is doing, you need to be able to read and understand it well enough that you can predict what it will do for any given input. That’s basically all “reasoning about code” is. If you can reason about your code, you can change it or add more features without breaking things or spending hours and hours cursing at your computer and howling “whyyyyy won’t this work?!”

So being able to reason about your code is really useful, but how do you do it? Practice, mostly. If you’re a beginner programmer you should not worry even a little bit about understanding a whole codebase or heck, even a whole class. Focus on one method or one loop or one if statement at a time. When you get enough practice, you’ll be able to understand those really quickly and you can move up a level to figuring out what a whole method does with different inputs or how two methods in the same class work together.

Oh, and it really helps if the code you’re trying to reason about is good code (that is, well organized, has good names, etc). Some code is next to impossible to reason about because it’s full of giant methods or the variable names aren’t helpful at all or, and this is one of the worst problems, variables change all the time in unpredictable ways. A “total” variable that changes value each time through a loop isn’t so bad, it’s clear what it’s for and why it changes. On the other hand a “total” variable that gets reused for completely different totals at different places in a method is a real problem. Humans can only hold so many things in their working memory at once and “wait where does total change again?” takes up most of them. If you have a terrible time reasoning about a certain piece of code, it’s entirely possible the problem is not you but the code.

In cases like that when I don’t have time to refactor the code so it’s easier to read I find it really helpful to make a lot of notes and draw myself a map through the code. If you want to be really helpful you can even type up your notes / make a diagram out of your map and add it to your developer documentation.

Reasoning about code can be hard to do and takes practice, but it’s not some sort of magic that only “real” programmers can do.

How does a thread work, anyway?

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Threads are used a lot in java, so I should probably understand how they actually work. They’re one of those things you use all the time without thinking about what’s really happening under the covers. I know threads and processes are related, but not exactly how.

First of all, what’s a process? To understand threads inside a process you need to understand processes first.

A process is an individual thing that’s separate from all the other processes running on your computer. In most cases a process is a single program running on your computer, but some programs have many processes – Chrome, for example, has a process for each tab. To quote the official tutorial on concurrency in Java: “A process has a self-contained execution environment. A process generally has a complete, private set of basic run-time resources; in particular, each process has its own memory space.” As I understand it, the separate memory space is the really important part of a process – this keeps processes from overwriting each other’s memory, crashing your computer, and wrecking your day.

Threads, on the other hand, are just parts of the parent process that execute semi-separately and all use the same memory. This means they can change a variable another thread just set, cause wildly bizarre bugs, and wreck your day. Every process has at least one thread, but can have more.

Okay, so why would you want to use threads when you could use processes to keep everything separate? Because processes use up a lot more system resources than threads, it’s more work to get them to communicate with each other, and they’re just overkill for a lot of problems. If you’re building in a search feature in your app and you want to search by a few different things (like name, address, and ID number) from one search box, creating a whole process for each search is way more work than you need to do when you could just use threads. Do you really want to write a whole separate program for each search? I sure don’t.

So threads are convenient, but what are they really? Saying they’re a single thread of execution through a program is all well and good, but what does that really mean? To quote stackoverflow: “A thread is a basic unit of CPU utilization; it comprises a thread ID, a program counter, a register set, and a stack.” Those things are also called the execution context, because they’re everything you need to know about the executing program to stop it and start it again in exactly the same state it was in. The CPU does that a lot so it can appear to do two things at once (if you have a multicore processor, it actually can do more than one thing at once). If one thread is waiting for data to come back from the database, which takes forever from the perspective of a CPU, the CPU will essentially make a note of where the thread got to in the code and what values all of its variables had, then start executing another thread using the “notes” it made about that one.

Because threads all share the same address space, they can share information really easily by updating global variables. In a process, a memory address (aka a variable) will probably mean nothing to another process. In a thread, any variable that’s in scope can be used and (if it’s not final) changed. This is really handy for stuff like web programming – if a thread that’s handling a particular HTTP request needs a reference to the database service, it can just grab one from the controller/servlet/general parent object that contains methods for handling individual requests.

When a thread completes, its variables get garbage collected as usual (assuming nothing else has a reference to them), you don’t have to do anything special to clean up after it.

And finally, while the tutorial I linked above talks about Thread objects and Runnables, in modern Java you mostly use CompletableFutures and let them handle starting and stopping threads for you.

Let’s play CPU!

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I think one of many reasons it’s so hard to learn to code is that the people doing the teaching have all forgotten what it was like not to know how to code, so we skip over some really important basic steps because we think they’re inherently obvious. Case in point, this poor redditor who nobody ever taught how to work through a piece of code with a pencil and paper. I had to read the question a couple of times to understand what they were even asking, it just didn’t occur to me that someone wouldn’t know how to trace through code manually.

The example that user posted was “x=0; y=0 While (x<7) { x=y-x; y=x+x; x= x+ y + 1;}”

First of all, let’s clean that up a little:

x=0;
y=0;
while (x < 7) {
    x = y - x;
    y = x + x;
    x = x + y + 1;
}

In the beginning x is 0, which is definitely less than 7 so we enter the loop.

Inside the loop, take each statement and swap out the variables for their current values and then do the math and put that value in the variable:

x = y – x becomes x = 0 – 0 becomes x = 0
y = x + x becomes y = 0 + 0 becomes y = 0
x = x + y + 1 becomes x = 0 + 0 + 1 becomes x = 1
At the end of the loop x = 1 and y = 0

Now we check the condition at the top of the loop again and x is still less than 7 so we go through the loop again

x = y – x becomes x = 0 – 1 becomes x = -1
y = x + x becomes y = -1 + -1 becomes y = -2
x = x + y + 1 becomes x = -1 + -2 + 1 becomes x = -2
At the end of the loop x = -2 and y = -2

At this point, I’m getting very suspicious this loop will never exit. I don’t think x is ever going to be greater than or equal to 7, but just to be sure let’s go through the code one more time

x is still less than 7 so we go through the loop again

x = y – x becomes x = -2 – -2 becomes x = 0
y = x + x becomes y = 0 + 0 becomes y = 0
x = x + y + 1 becomes x = 0 + 0 + 1 becomes x = 1

At the end of the loop x = 1 and y = 0. These are the same values we had after we went through the loop the first time, so now we can be completely sure the loop never ends. After each time through the loop x is either 1 or -2, there’s no way for it ever to be 7 or more.

That’s it. Working through code with a pencil and paper is just keeping track of what values all of your variables have and swapping out variables for their values. It’s really tedious, that’s why we make computers do it :) And to be clear, you’re never expected to be able to work through complicated code like that purely in your head. Everybody else needs a pencil and paper too, there are just too many details to keep them all in your working memory.

Okay, so if working through code with a pencil and paper sucks so much, why does anyone do it? Because it gives you a really solid understanding of what the computer is doing, which you’ll need later when you start building more complicated things. For a simple loop like the one above you can just throw that snippet of code into an IDE, run it, and see what happens, but you can’t even start building bigger things without a foundation of knowing what the computer is doing when it runs your code.

Project of the day

Somehow I came across a link to this one episode of a podcast called Reply All. That particular episode is about Anxiety Box, a delightfully odd project by Paul Ford. He was dealing with some pretty serious anxiety and being a nerd, decided to write a program to be anxious for him. It’s a really interesting story, and while Anxiety Box is now defunct, all the code is available so you can run your own external jerkbrain if you like.

Repetition is underrated

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The more I read about the struggles beginner programmers have and the more I mentor at Ladies Learning Code workshops, the more I think that repetition is seriously underrated when it comes to teaching anything technical.

When you’re learning a language or an instrument or a sport or a physical skill like plumbing or carpentry or even math, which is similar to programming in a lot of ways, you expect to have to repeat the same thing multiple times before you remember all the details and get it right every time, but somehow when you’re learning to code we assume you should only need to be told how a for loop works once and you’ll understand it perfectly right away and remember it forever. That’s just not how our brains work and that’s why I think repetition is so underrated.

It is completely normal to need to write a lot of for loops before you get it right every time. Some people do pick up programming concepts very quickly but that doesn’t mean you’re dumb or abnormal if it takes you longer. Something like a for loop (or anything programming construct) seems simple once you understand it, but there are actually an enormous number of fiddly little details you have to keep track of to get your loop to work. You know what’s a great way to learn all of those details so thoroughly you hardly even think about them anymore? That’s right, repetition!

Programming isn’t just a matter of understanding the concepts, you’ve also got to learn them so thoroughly you don’t have to think about how to write a loop, you just write one when you need it. Without that thorough of an understanding, programming is like trying to speak another language by looking up each word individually in your [other language] to English dictionary. That’s one way to learn, but you’ll probably just be miserable and frustrated and forget what you were trying to say in the first place before you’re even halfway through your sentence.

Come to think of it, maybe the kind of drills you do when you’re learning a language could help people learn to program without spending so much time worrying that they’re just not smart enough.

Anyway, repetition is seriously underrated and I wish we collectively talked more about how much practice it takes just to pick up the basics of programming, let alone the complicated stuff like deciding how to structure your code or what to name things (still one of the hardest problems in programming :) ) I think a lot of programming tutorials assume that you know you need to practice without explicitly saying it or without making it clear just how much practice you need. I have to admit I wouldn’t want to write pages and pages of very similar programming exercises either, but it’s not so hard just to say that programming takes practice and you’ll probably need to go through the tutorial a few times before it sticks.

If you did a tutorial or a workshop just once and didn’t instantly become a good programmer, congratulations, you’re normal! If you keep at it, you’ll get there.

Link of the day

Today’s link is a reminder that no matter how great you think your favourite language is, every language has flaws. Some people like to go around talking about how their favourite language is the best language and every other language sucks, but that’s much more about personal preference than it is about any one language being objectively better. Different languages are good for different things anyway.

Read a little YourLanguageSucks and don’t be a jerk about other people’s favourite languages :)

Let the computer do it for you

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Many years ago when I was in college, a friend taught me something that’s been really useful for my whole career. That lesson was to let the computer do it for you. Unless there’s a compelling reason to do things the hard way, just let the computer make things easier for you.

Learning lisp? Get a plugin for your text editor or a simple IDE like Dr Racket that matches your parens for you.

Working with fixed width files? Get Record Editor, it’ll save you so much time!

Fighting with javascript? Get WebStorm! Seriously, it’s freaking amazing.

If you have to do something tedious and fiddly, get the computer to help you. That’s what it’s good at. There is a tool out there that will make your life easier, you just have to go and look for it. The hard part is remembering to go look for it :)

It’s normal to think that if there was a tool you could use your teacher or your boss or someone on your team would have told you about it, but thinking to look for tools like that is surprisingly unusual. And to be fair, it can be a real timesink to try tool after tool just to find out none of them are better than what you’re already using.

That said, if someone on your team hasn’t already told you that they’ve tried everything they could find (and searched for tools recently), it’s worth doing at least a little Googling and seeing if there’s already a tool that would make your life easier. Other people use lisp, you can safely assume there are tools out there for it. Other people use fixed width files, you can safely assume there are tools for those too. And tons of other people use javascript, tools for that are getting better all the time.

If there isn’t already a tool, you might be able to build one. That’s exactly what bash or powershell scripting is for – fiddly things that humans are bad at and tedious but simple things that humans just don’t wanna do. If you’ve ever run a build script, you’ve used a custom tool that someone wrote to automate building your application so it gets done the exact same way every single time. No matter what OS you’re running, there will be other scripts out on the internet that you can take apart to build your own custom tools.

Whether you find tools or build your own, remember that boring stuff is the computer’s job!

Link of the day

How do you know when to take someone’s advice and when to ignore it? Today’s link lays out a few simple steps to figure out When ignoring advice makes sense. There’s no shortage or advice for programmers out there, but there’s just no way all of it works for every single programmer. If you have a process for evaluating advice, you can be sure that the advice you reject really doesn’t work for you. If you just flail around and try stuff, well maybe the things you don’t like really don’t work for you, but on the other hand maybe they just feel weird and that makes you want to stop and go back to normal before you’ve really given them a chance.

Go forth and ignore some advice, safe in the knowledge that you gave it a fair shot and it really didn’t work for you :)

Rich Hickey – Hammock Driven Development

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A little while ago a friend of mine shared this list of Talks that changed the way I think about programming in one of the many Slacks I’m in and I finally started watching them.

Here’s my recap of one of the talks from that list, Hammock Driven Development by Rich Hickey. In it he describes his process for solving hard problems, which is obviously a huge part of what programmers do and is probably useful for just about anyone else too. There are a couple of technical examples in the talk but almost all of it should make sense to a non-programmer.

I put numbers on these steps to make this blog post easier to follow, but that doesn’t mean you have to follow this process in this exact order. The first couple of steps really do need to happen first, but after that you may want to iterate over the remaining steps a few times and possibly even go back to the beginning to make sure that you really do understand your problem in the context of all the new stuff you’ve learned while you were trying to solve it.

Step 1: state the problem. Say it out loud, talk with team member about it, write it down if nothing else.

Step 2: understand the problem. What do you know already (facts, context, constraints)? What don’t you know? For example, if you know you will need input data, where does it come from? if the primary source goes down, is there a secondary? Are there related problems? Hint: there are. Your problem is almost certainly not unique in the history of the world. And if you’re going to bother to figure all that stuff out, write it down!

Step 3: be discerning. Not everything is awesome! Look for problems in your proposed solutions and try to solve those too right away up front. Do you think there aren’t any tradeoffs in your proposed solution? Not likely, it’s much more likely you’re missing something. You should have questions – nobody knows everything! If you don’t have questions, you’re missing something. Write all this stuff down too.

Step 4: more input better output. You can’t connect things you don’t know about. Read in and around your space (not just your exact problem, also similar stuff so that you can let that simmer and let your brain make connections). Look (critically!) at other solutions too. Great solutions can come from tearing apart someone else’s idea.

Step 5: tradeoffs. Everybody says design is about tradeoffs, but you need to look at at least two possible solutions and figure out what’s good and bad about those things before you can really say you made a tradeoff. Write this down too! You may be seeing a theme here :)

Step 6: focus. This is where the hammock comes in. One of the great things about the hammock is that if you lie down with your eyes closed, no one knows you’re not sleeping and they won’t bother you because you might be sleeping so you can focus completely on your problem without interruptions. The computer is a prime source of distractions – you need to get away from the computer if you want to focus. You can’t do everything – if you really focus on something you’ll drop other balls like returning phone calls or emails, or remembering to run that errand or fix that bug you said would be really quick. Let your loved ones know what you’re doing and why you’re not going to be super responsive for a while (as an aside I really liked this point about treating people who matter to you as if they, you know, matter to you). An interesting detail Rich includes in this step is that you should close your eyes to really focus – at this point you’re not looking for any external input at all

Rich has a bunch of interesting stuff to say about what he calls your waking mind and your background mind (in the Leaning How to Learn course they call it focused and diffuse modes of attention, if you’ve taken that course this will all be pretty familiar). He uses his waking mind to assign tasks to his background mind and to analyze it’s products. Your background mind is where you solve most non-trivial problems but you can only feed it, not direct it. You need to spend enough time thinking about something for it to become an agenda item for your background mind to get anything useful from it.

Step 6 has two substeps, loading up your background mind and then letting it work. To load up your background mind you review everything you wrote down in the previous steps and really focus on it. Because your waking mind can only keep track of so many pieces of information at once (7 +- 2, as far as I know), you need to have written everything you know about your problem down so you can swap those pieces back into your working memory when you need them. To load all of this into your background mind you need to survey everything you’ve written down to give your background mind the chance to make connections between different things that your working mind didn’t realize could be connected. Rich stresses that you can’t do this at the computer, you need to go somewhere and have no external input. He recommends going somewhere you can close your eyes but not go to sleep so you can sort of switch your brain from external to internal input(all that information about your problem that you just reviewed).

The other substep is to leave the problem alone for a while and let your background mind do its thing. Sleep is a great way to do this, or going for a walk, or anything that gets your waking mind off of the problem. If you’re working on a hard problem you should sleep on it for at least one night, more if it’s a really hard problem. Just because you have an idea right away doesn’t mean you won’t have a better one in the morning. And once you have an idea, analyze it, don’t just run with it. Just because you slept on it doesn’t mean that solution that popped into your head in the morning is perfect.

Optional step 7: don’t stay stuck. If you have another problem to work on, do that when you feel stuck instead of just sitting there and staying stuck. If you don’t have another problem or really need to stay focused on your current one, gather more input, talk with more people if you can, and go through the whole process again.

A caveat to this whole process is that if you do have more than one problem you’re working on, you may spend hours loading up all the information about one problem and wake up the next morning with the answer to a different problem. That’s a thing you just have to accept, brains are funny sometimes. If you can’t switch to the other problem, at least write down the solution you came up with before going back into gathering information and loading it up for the problem you really want to solve.

Rich’s talk is really good and I highly recommend watching it yourself, but if you don’t have 40 minutes to dedicate to sitting in front of your computer then I hope this recap was helpful.

Link of the day

Today’s link is a companion to my earlier post with resume advice. After resumes come interviews, and in those you’ve got to ask your interviewer a few questions. When you’re just starting out it’s really hard to know what’s okay to ask or what you would even want to ask. Fortunately Jen Hamilton compiled a fantastic list of questions to ask interviewers from various sources (they’re linked at the bottom) and her own interests and experiences.

A couple of questions I’d like to highlight are these ones:

Flex time/core hours? Is variability tolerated or is everyone expected to be on the same schedule?

Is it possible to work from home, say, 1 or 2 days a week? Does anyone do this?

Just because a lot of companies that hire developers work normal 9-5 hours doesn’t mean they all do. I’ve heard enough horror stories to strongly recommend asking exactly when you are expected to be in the office/available online and whether it’s going to be a big deal to work from home to let the field tech in to fix your internet connection.