Posts tagged with "Coding"

This post is very much a case of me writing it down to try and get it all straight in my head, and to make sure it sticks. The other day I was reading about Swift's types and type-equality checks, and as I'd expect from plenty of other languages I've worked with, there's a way for checking that two types are the same, such that super/subclasses aren't taken into account, and a way where they are. So, given this silly code:

class Animal {}

class Cat : Animal {}

print( Cat.self == Animal.self )          // False
print( Cat.self is Animal.Type )          // True
print( type( of: Cat() ) is Animal.Type ) // True

it's made clear that == checks for strict equality and a super/subclass relationship isn't taken into account. On the other hand is does take it into account.

Only... what's with this whole .self sometimes and .Type other times business? That took a little bit of writing code and playing to get comfortable with. Here's how I understand it now (and do feel free to correct me below if I'm way off):

Given the above code, Animal.Type is the type of a value that expresses the type of Animal. On the other hand, Animal.self is a value that is the type of an Animal. Yeah, I know, that still reads oddly. But written as code:

let feline : Cat.Type = Cat.self

I think it makes a lot more sense. And having got there I felt I better understood it. I'm not 100% sure I'm 100% with it, but I'm getting there.

I'm going to file this one under "it seems really unnecessary, but it's also kinda cool". While reading up about protocols the book I'm reading introduced the ExpressibleBy*Literal protocols, where the * is one of a number of obvious literals. For example: ExpressibleByStringLiteral. As you might imagine, it lets you create a class that can be initialised with a literal value, as opposed to needing to appear to call the constructor for a class.

So, for a silly example:

class Hello : ExpressibleByStringLiteral {

    private let what : String

    required init( stringLiteral what : String ) {
        self.what = what
    }

    func say() {
        print( "Hello, \(self.what)!" )
    }
}

You could, of course, write this:

let v1 = Hello( "world" )
v1.say()

but because of ExpressibleByStringLiteral you can also write:

let v2 : Hello = "universe"
v2.say()

Now, sure, in this case it saves you nothing, but this does also mean that parameters of functions whose type uses one of the `ExpressibleBy*Literal protocols can be passed a literal, rather than a "long-hand" instantiated object. For example:

func Greet( _ h : Hello ) {
    h.say()
}

Greet( "davep" )

I can see that being quite handy.

I'm going to file this one under "it makes perfect sense, but I don't think it aids in making the code readable" -- something which I'm finding is a bit of a theme with Swift.

In Swift self gets used and gets used in a way you'd expect from many other languages. So far so good. But, it seems, Self is also a thing too, and it's different from self. Whereas self is the current instance, Self is the current type. So consider this:

class Greeting {

    class func message() -> String {
        "Ayup!"
    }

    func message() -> String {
        "Well hello there"
    }

    func emit() {
        print( Self.message() )
        print( self.message() )
    }
}

Greeting().emit()

When run, the output is:

Ayup!
Well hello there

It makes sense that that's the case. I actually really like the ability to use Self rather than having to use Greeting, but damn that's really setting things up for either mistyping or misreading code. You're going to want to hope that your development environment makes it super obvious what's a value and what's a type when it comes to using font choices.

Some languages favour a "one way to do it" approach, some favour "there's more than one way to do it". I'm not sure I'm at a point where I have a feel for what Swift's approach is, but I'm getting the impression it's more the latter than the former.

If there was one thing that made me think that, it was when I found out that Swift's bool type has a toggle method.

var cool = false

print( cool )
cool = !cool
print( cool )
cool.toggle()
print( cool )

giving:

$ swift run
false
true
false

I can see a number of reasons why that's actually going to be handy -- the main one being when you want to throw around a toggling method -- but it still struck me as rather odd on first reading. I also think it's worth me making a personal note about it because foo.toggle() isn't going to stand out as much as foo = !foo when reading code. At least not for a short while.

Today's little "Swift TIL" is observers. While reading up on the language I was delighted to find that it has observer support baked right into the language, for any sort of variable. So code like this:

var name  = "David" {

    willSet( new ) {
        print( "About to change name from \(name) to \(new)" )
    }

    didSet( old ) {
        print( "Name changed from \(old) to \(name)" )
    }
}

name = "davep"

Does what you'd imagine:

About to change name from David to davep
Name changed from David to davep

Not only can I see how that'd be useful for the main sorts of purposes that Swift is put to, I can think of many times when I'd have benefitted from that in my general day-to-day work. Of course, you can create an observer approach in any language really, but having an idiom that's part of the language feels nice and tidy.

Following on with writing little notes to myself so I remember some key things as I learn about Swift...

I sort of feel like this will make reading code a little harder, so it's one I want to keep in mind. When calling an instance method, if it's not ambiguous, you can omit self. from the call. For example:

class Foo {
    private func inner() -> String { "Foo" }
    func outer() -> String { inner() + self.inner() }
}

print( Foo().outer() )

This makes me feel a little uneasy, and I strongly suspect I'll always use self. when writing such code: I'm a big fan of the idea that we write code for people, not for compilers.

As I mentioned yesterday, I'm going to make a small series of posts where I write down things that I've stumbled on while getting to know Swift that are, for me personally, worthy of note, different, unusual, cool, or just simply "WTF!?!".

Because learning new stuff is fun.

My first one is that you can use keywords as identifiers if you "escape" them with backticks. Kind of like this:

let `let` = "let"

print( `let` )

I'm struggling to imagine a situation where I'd ever want to do this. I'm still unsure if my reaction is "that's cool" or "WTF?!?".

It's five years ago this month that I bought myself my first macOS (then OS X) device. After many years of having a Windows machine as my daily driver, which was also my work machine (I worked from home), I decided it was high time that I returned to having a Unix-a-like system on my desk too. For a decade or so, starting in the later-90s, I'd had a GNU/Linux desktop. I still had a Windows desktop (until a couple of years ago most of my work was on DOS and Windows), but thanks to the wonders of a KVM, and later an X server that ran on Windows, my personal hacking was done on a GNU/Linux desktop.

But as things moved around, priorities changed, as life moved on, the GNU/Linux boxes got retired and never quite replaced. Eventually, in 2015, I found myself with the means and desire to recover that sort of setup. Long story short, after a lot of reading up and weighing up options I decided that the best option for a desktop Unix was... an iMac!

I loved it. Sure, there were lots of little things on the surface that were different or annoying or just plain not as cool as the Mac fans would tell you, but under the hood I found what I needed: a Unix CLI with all the things I knew well. And, of course, it ran GNU Emacs just fine; that was the really important thing for me.

Pretty much right away I decided that it might be fun to learn the tools necessary to develop native Mac apps, and perhaps even iOS apps. I downloaded XCode, bought a book, and started working through it. Having got that book, I decided it might be interesting to own an iOS device too. So, sort of needing an MP3 player, and having no wish to get an iPhone, I got myself an iPod Touch. So I was all set to devour the Swift book, write some stuff for OS X, create an iOS app or two, and... life happened. Stuff cropped up that distracted me from taking that further and I never really returned to working through the book.

Fast forward to now and that initial iMac and iPod purchase spiralled a wee bit. Next after the iPod was an iPad Mini, when my Nexus 7 was starting to show its age and it was obvious that Google wasn't going to produce any more good Android tablets. Then, when I needed a very portable Unix-a-like machine for trips between where I was living and Edinburgh, I got myself a MacBook Air. Since then the iPod Touch has been replaced once, as has the iPad Mini. I now also own an iPad and a MacBook Pro. Unless Apple screw up and turn Macs into something unusable for developers (there are rumours), I imagine I'll be using Apple devices for some time to come now.

And then, last month, having finally got frustrated with where Google were going with Android and the Pixel series, I jumped ship to the iPhone 11.

As of right now I'm in a situation where I'm all about the Apple ecosystem regarding hardware and operating systems (including for my work machine), all of which is there to support my heavy use of the Google ecosystem (actually, the one bit of Google hardware I still lean on heavily is the Google Home -- I have 3 around my home).

So... given all of that, I thought it was time to look at returning to learning Swift, with a view to writing some native macOS and i(Pad)OS stuff. I soon realised that the book I'd bought back in 2015 was rather out of date. It covers Swift 1.2 -- we're now up to 5.2! Given this, and given I've forgotten pretty much everything I'd read at the time, I decided I should start again from scratch.

This weekend I've started reading my way though iOS Programming Fundamentals with Swift. While this obviously has an emphasis on iOS, I'm already finding that the first part of the book is a really great introduction to the Swift language in general. The pace seems just right, and the way topics are grouped makes it easy enough for me to skip over what's obvious (I don't need to know what objected-oriented programming is, and what the difference between a class and an object is, etc) and read up on the detail of this particular language when it comes to general concepts I know (knowing the differences between a class, struct and enum in the language is important, for example).

I've yet to write a line of code, but I'm fine with that. The book is spending a lot of time introducing the language before encouraging you to fire up XCode, and I'm okay with that. I'm never a fan of being asked to write out code that I can't properly follow -- that just makes stuff look like magic when it's far more educational to know what's going on. What I am finding is I'm making lots of notes that are either "oh, yeah, this is cool, I like this idea!" or "WTF are you kidding me?!?". Which is really nice -- it's always great to learn a new language that's a bit different from what you normally use.

My plan then, over the next few weeks, it to keep at this and hopefully document my journey. I think I'd like to write a short series of TIL-type posts; nothing too long, just some new thing I read or discovered and my reaction to it. So, if you happen to follow this blog, I apologise in advance for any Swift-spam.

You have been warned. ;-)

Late on last year I stumbled on an article about Dnote. Annoyingly, I can't recall now where I saw it, but I made a reminder to look at it over my Christmas break.

Dnote looked like a tool that would fill a hole I had in how I work. When it comes to making notes about things, and keeping things for future reference, I use a few tools, each one being just right (for me) for the job in question. I use Evernote to track documents and other household type things. I use Keep to make notes about stuff I need to remember short-term (say, the size of a space in my bedroom that I want furniture to go in) and also to record notes while in meetings at work. I use Journey to keep a journal about... anything, really. Finally, I use Pinboard to keep hold of URLs I might want to go back to (I also use it to create a to-read list).

Amongst all of this, however, I felt I was missing something for keeping track of things that don't really fall into any of the categories above. Mostly this would be work-based or hacking-based things that are short and sweet but I don't always use enough to easily remember. I wanted just the right tool that would let me ferret away useful one-liners, remind myself of obscure switches that get used once or twice a year, etc.

After reading up on Dnote it seemed pretty clear that this was just such a tool.

After getting back to the office at the start of this month I decided to make use of it and see how it went. My idea was simple: I'd record any "TIL" stuff that I might want to remember in the future, as well as recording things I need now and again but can't always remember.

So far it's working quite well. I like that it has a simple CLI. I like that it's got a backend that you can use to sync between different machines. I like that it's got a web interface that's mobile-friendly. I like that it's Free Software and so you can host your own server if you wish.

I found I liked it enough that, of course, I felt the need to start a simple Emacs wrapper for the CLI.

At the moment dnote.el is designed to be a simple capture system. There are commands for capturing a one-liner (entered in the Emacs mini-buffer), for capturing the content of the current buffer, and for capturing freshly-entered multi-line text, entered in a buffer that uses markdown-mode. There's also a command for syncing notes if you have configured Dnote to talk to a backend.

What I don't have right now is the ability to navigate and view notes. So far I've not really felt the need for that because the CLI approach works so well. Longer-term though I can see my tweaking this and adding in commands for searching, viewing, editing and deleting notes.

But, for now, if you've not had a look at Dnote, I'd highly recommend having a play and seeing if it makes sense for you. And, if it does, and you're an Emacs user, perhaps dnote.el will be useful too?

Both at work and at home I use Emacs by keeping a copy running all the time, and use emacsclient to open files inside it (including on remote machines thanks to a bit of ssh and heavy use of tramp -- I might write this up at some point). This works really well, but does mean I tend to build up a lot of buffers over time.

Having lots of buffers open isn't generally an issue, and if I'm working on lots of different files in a project during the course of a hacking session it's actually a good thing. But, quite often, I want to tidy up the buffer list, clearing it back to near-zero buffers open. Many years ago, when I had a "proper" tower system running 24/7, with Emacs open all the time, I'd use clean-buffer-list as part of midnight. Along the way that fell out of favour with me, likely because I drifted into using machines that had Emacs open all the time but where the machine wasn't awake all the time.

Eventually I decided to have some fun rolling my own solution, and nuke-buffers was born.

Rather than try and do things in an automated way, this was designed to be bound to a key (or two) and then be run when I wanted, being as harsh as possible about cleaning up the buffer list. Since first writing it it's worked well for me.

These days I tend to let the buffer list build up as I work on a new feature, or chase down a bug, etc. Then, once I've made the final commit for that period of focus, I'll hit the nuke-buffer key combo as the final act of confirming that I've done the job. So not only does this help tidy my Emacs session a bit, it also feels like a physical form of punctuation -- back in less sensible days, when I had some terrible habits, it would have been when I'd reach for the celebratory cigarette; buffer-tidying feels far more wholesome. ;)

The way the code works is, of course, mostly directed at how I work -- it's highly likely it wouldn't make sense for many other people. The main aim is to kill as many buffers as possible, but without disturbing anything else. The list of buffers it gathers for nuking avoids buffers that are visiting files but have unsaved content, avoids the minibuffer (obviously), avoids any "special" buffer (one that starts with a space then an asterisk), avoids the current buffer and also avoids any buffer in a list of names to avoid.

I've being using this on a daily basis for around 2.5 years now and it's done the job without ever losing me any work.