I just heard someone using the phrase “first-class citizen” in a programming podcast, and that led me to ponder the use of that phrase. The podcast was Swift Package Manager SuperPowers from Empower Apps. Empower’s a great podcast, this is a great episode, and the idea of first-class citizenship comes up only in passing and is basically immaterial. But not to this post!
Whatever the situation that leads someone to say “first-class citizen”, there’s a value judgement being made: this thing is good, because it is more conformant to the (probably unspoken) rules of the road of the ecosystem, platform, or whatever the thing is supposed to be a citizen of.
Many of us in the privileged software engineering world live in societies that do not have overt “levels” of citizenship. That said, there still are multiple levels: nationals, resident aliens, temporary visitors, and prisoners may all have different rights and responsibilities. And in societies where there are still explicit or tacit class hierarchies, making reference to them is often somewhere between impolite and offensive. So this idea of “first-class citizenship” comes with a big side-wink: it’s a first-class citizen, we both know what I mean.
An obvious way for a technology to be a first-class citizen of something is for it to be made, distributed, or otherwise blessed by the maker of the something it’s a citizen of. That’s the context in this show: Swift Package Manager is a first-class citizen of the Apple software development platform because it’s a first-party component. Now, it’s a first-party component with the job of giving access to third-party components, so there’s a limit to the vendor ownership, but nonetheless it is there.
In this sense, first-class citizenship confers clear benefits. If someone is already playing in the Apple tools sandpit, they already have access to SwiftPM. They may not already have access to CocoaPods, so the one step “fetch all the packages” becomes two steps: fetch the package tool, then fetch all the packages.
That bit is easier, but it evidently isn’t sufficient. Is the other tool better at fetching packages correctly, or better for writing packages, or more secure, or easier to use? When we say “better”, better at what, and for whom?
It’s possible for something that is first-party to not be first-class. Mac OS X came with the Tcl language for a couple of decades but I can’t find evidence online that it was ever referred to as a “first-class citizen” of the Apple ecosystem. In 2022 you wouldn’t call OpenDoc or the Macintosh Runtime for Java first-class citizens either, because the vendor no longer supports them. Actually it’d be an interesting exercise to take an old Apple Developer Connection CD (the earliest I have will be from around 2005), and find out how much of that content is still supported, and of that subset how much you could get broad agreement for the first-class nature of. I’d be willing to bet that even though ObjC is still around, distributed, supported, and developed, a decent chunk of the community would think twice about calling it first-class.
But then, it’s also possible for things that are third-party to be first-class. Apparently, Java is a first-class citizen in a Docker ecosystem now. And Data should be a first-class citizen in the Enterprise (this is, by the way, a spoiler for the Star Trek: The Next Generation episode the measure of a man).
When third-party things are first-class, we’re saying that going the extra step of getting this thing you don’t already have is better than stopping here and using what you already own. Again we have the questions of better at what and for whom. Really any of this stuff lies on a continuum. Consider a database. You use a database because it’s cheaper, faster, and better to turn your stuff into the database’s model and use the database vendor’s structures and algorithms than it is to design your own efficient storage and retrieval format. If you could do that well (and that’s a big if) then your hand-rolled thing would probably be better for your application than the database, but also all maintenance work falls onto a very small community: you. On the other hand you could use whatever comes in the box, which has the exact opposite characteristics. They each have different types of first-classness.
And then there’s a (very old, but very common) definition of a data type being first-class or not depending on whether they can be represented by variables or expressions. So when Javascript developers say “functions are first-class citizens in Javascript”, they mean that JS has a feature that ALGOL did not.
