[jcelerier]

> capabilities similar to -- and at least as powerful as -- type templates, value templates, constexprs, concepts, and conditional compilation (preprocessor), with a single feature and keyword

are you sure ? zig does not seem to have something that looks like concepts (an issue is open : https://github.com/ziglang/zig/issues/1268) nor a way to put restrictions on a given type passed to a function or series of function.

e.g. it seems that what in C++ would be (with concepts, but the same can be written more verbosely with C++03 templates if needed)

    void f(IsFoobar auto x) {
     
    }
    void g(IsFoobar auto y) {
     
    }

would require in zig to have a comptime test for the "foobar" nature of T in every function, which looks like a downgrade and does not expose the requirements cleanly in the function interface.

[AndyKelley]

Here's the C++ example from the article:

    template <class T>
    concept SignedIntegral = std::is_integral_v<T> &&
                            std::is_signed_v<T>;
    template <SignedIntegral T> // no SFINAE here!
    void signedIntsOnly(T val) { }

Here's the equivalent Zig code. You can run this with `zig test example.zig`.

    const std = @import("std");
    const assert = std.debug.assert;

    fn signedIntsOnly(val: var) void {
        comptime assert(std.meta.trait.isSignedInt(@TypeOf(val)));
    }

    test "concepts example" {
        var x: u32 = 1234;
        signedIntsOnly(x);
    }

This produces the compile error:

    ../lib/std/debug.zig:221:14: error: unable to evaluate constant expression
        if (!ok) unreachable; // assertion failure
                 ^
    ./example.zig:5:20: note: called from here
        comptime assert(std.meta.trait.isSignedInt(@TypeOf(val)));
                       ^
    ./example.zig:10:19: note: called from here
        signedIntsOnly(x);
                      ^
    ./example.zig:8:26: note: called from here
    test "concepts example" {
                            ^
    

It accomplishes the same thing, just a bit more verbose, since it is using the general tools of the language rather than special syntax.

[jcelerier]

> assert(std.meta.trait.isSignedInt(@TypeOf(val)));

well yes, that's my point. You could also write

    void signedIntsOnly(auto val) {
        static_assert(std::is_integral_v<T> && std::is_signed_v<T>); 
    }

in C++ but it's quite preferable to refactor this inside the types themselves (for the same reason that you want to refactor any other kind of code in general - besides you don't want to go read the implementation of your functions every time do you ? IDEs show us only prototypes for a reason).

How would you for instance specialize a generic function in Zig ? Does zig accept

    fn complexmathoperation(val: var) void {
        if(isInt(@TypeOf(val))) { 
        }
    }

and in another module

    fn complexmathoperation(val: var) void {
        if(isSomeKindOfLibrarySpecificMatrix(@TypeOf(val))) { 
        }
    }

and properly dispatches between both ?

I'd be hard pressed to say that it is "as powerful" given what I'm seeing for now.

[pron]

> besides you don't want to go read the implementation of your functions every time do you ? IDEs show us only prototypes for a reason

The IDE can be changed to show you assertions in addition to the signature, just as it also shows doc comments. That the signature is special isn't some law of nature, it's just habit (and users of untyped languages don't even have those).

> How would you for instance specialize a generic function in Zig ? ... and properly dispatches between both ?

No, you'd need a single definition with a comptime branch.

> I'd be hard pressed to say that it is "as powerful" given what I'm seeing for now.

What you're seeing is personal taste. In my taste, that Zig doesn't allow overloading and has clear dispatch is clearer is more preferable (in fact, it's touted as one of Zig's biggest strengths); in yours, it is less preferable. That's perfectly OK, but it's got nothing to do with expressive power (which has a pretty good and precise definition: https://youtu.be/43XaZEn2aLc). There is a reason why some languages are more complicated while others are simple -- some people aesthetically prefer the more complex languages while others prefer simpler ones. What is impressive about Zig is that despite being simple, it's not giving up power, at least in those aspects I mentioned. C, another simple language, cannot do those things.

[pron]

> zig does not seem to have something that looks like concepts ... nor a way to put restrictions on a given type passed to a function or series of function.

Of course it does. Just place a comptime assertion on the @TypeOf a var.

> would require in zig to have a comptime test for the "foobar" nature of T in every function, which looks like a downgrade and does not expose the requirements cleanly in the function interface.

Cleanliness is a matter of personal aesthetic preference, and a rich type specification "in every function" is not less work or less clear than a comptime assertion in every function. In either case you get a clear compilation error. Requirements are never fully specified in the function's interface unless you have dependent types or contracts (both with their own problems and tradeoffs). Even Haskell has partial subroutines. What portions of the spec that is already enforced at compile type should be exposed in the signature -- keeping in mind that it will never be all of them -- is a matter of taste. Zig might shift things around a bit, but the capability to enforce a specification that is at least as strong as structural types at compile-time is already there.