←back to thread

Things Zig comptime won't do

(matklad.github.io)
458 points JadedBlueEyes | 3 comments | 20 Apr 25 15:57 UTC | HN request time: 0s | source
Show context
pron ◴[20 Apr 25 18:16 UTC] No.43745438[source]▶
Yes!

To me, the uniqueness of Zig's comptime is a combination of two things:

1. comtpime replaces many other features that would be specialised in other languages with or without rich compile-time (or runtime) metaprogramming, and

2. comptime is referentially transparent [1], that makes it strictly "weaker" than AST macros, but simpler to understand; what's surprising is just how capable you can be with a comptime mechanism with access to introspection yet without the referentially opaque power of macros.

These two give Zig a unique combination of simplicity and power. We're used to seeing things like that in Scheme and other Lisps, but the approach in Zig is very different. The outcome isn't as general as in Lisp, but it's powerful enough while keeping code easier to understand.

You can like it or not, but it is very interesting and very novel (the novelty isn't in the feature itself, but in the place it has in the language). Languages with a novel design and approach that you can learn in a couple of days are quite rare.

[1]: In short, this means that you get no access to names or expressions, only the values they yield.

replies(7): >>43745704 #>>43745928 #>>43746682 #>>43747113 #>>43747250 #>>43749014 #>>43749546 #
1. baranul ◴[21 Apr 25 08:26 UTC] No.43749546[source]▶
Comptime is often pushed as being something extraordinarily special, when it's not. Many other languages have similar. Jai, Vlang, Dlang, etc...

What could be argued, is if Zig's version of it is comparatively better, but that is a very difficult argument to make. Not only in terms of how different languages are used, but something like an overall comparison of features looks to be needed in order to make any kind of convincing case, beyond hyping a particular feature.

replies(1): >>43754886 #
2. cassepipe ◴[21 Apr 25 18:22 UTC] No.43754886[source]▶
You didn't read the article because that's the argument being made (whether you think these points have merit) :

> My understanding is that Jai, for example, doesn’t do this, and runs comptime code on the host.

> Many powerful compile-time meta programming systems work by allowing you to inject arbitrary strings into compilation, sort of like #include whose argument is a shell-script that generates the text to include dynamically. For example, D mixins work that way:

> And Rust macros, while technically producing a token-tree rather than a string, are more or less the same

replies(1): >>43759831 #
3. baranul ◴[22 Apr 25 07:21 UTC] No.43759831[source]▶
The comment made by me, is a reply to another reader, not of the article directly. The push back was on the nature of their comment.

> the uniqueness of Zig's comptime... > You can like it or not, but it is very interesting and very novel...

While true, such features in Zig can be interesting, they are not particularly novel (as other highly knowledgeable readers have pointed out). Zig's comptime is often marketed or hyped as being special, while overlooking that other languages often do similar, but have their own perspectives and reasoning on how metaprogramming and those type of features fit into their language. Not to mention, metaprogramming has its downsides too. It's not all roses.

The article does seek to make comparisons with other languages, but arguably out of context, as to what those languages are trying to achieve with their feature sets. Comptime should not be looked at in a bubble, but as part of the language as a whole.

A language creator with an interesting take on metaprogramming in general, is Ginger Bill (of Odin). Who often has enthusiasts attempt to pressure him into making more extensive use of it in his language, but he pushes back because of various problems it can cause, and has argued he often comes up with optimal solutions without it. There are different sides to the story, in regards to usage and goals, relative to the various languages being considered.