[WalterBright]

> the notion of a comptime variable (for which I couldn't find an analogue in D)

A comptime variable in D would look like:

    enum v = foo(3);

Since an enum initialization is a ConstExpression, it's initialization must be evaluated at compile time.

A comptime function parameter in D looks like:

    int mars(int x)(int y) { ... }

where the first parameter list consists of compile time parameters, and the second the runtime parameters.

D does not have a switch-over-types statement, but the equivalent can be done with a sequence of static-if statements:

    static if (is(T == int)) { ... }
    else static if (is(T == float)) { ... }

Static If is always evaluated at compile time. The IsExpression does pattern matching on types.

[pron]

A comptime variable in Zig isn't a constant whose value is computed at compile time (that would just be a Zig constant) but rather variable that's potentially mutable by comptime: https://ziglang.org/documentation/master/#Compile-Time-Varia...

This is one of the things that allow the "comptime language" to just be Zig, as in this example: https://ziglang.org/documentation/master/#Case-Study-print-i...

[pcwalton]

You can mutate variables at compile time in D. See the compile time Newton's method example: https://tour.dlang.org/tour/en/gems/compile-time-function-ev...

[pron]

I don't think that's the same thing (rather, it's more like ordinary Zig variables in code that's evaluated at compile-time), as there's no arbitrary mixing of compile-time and runtime computation. Again, compare with https://ziglang.org/documentation/master/#Case-Study-print-i...

Anyway, I found this article that concludes that D's compile time evaluation is equivalent in power to Zig's, although it also doesn't cover how comptime variables can be used in Zig: https://renato.athaydes.com/posts/comptime-programming

However, as I've said many times, knowing about the theoretical power of partial evaluation, what excites me in Zig isn't what comptime can do (although I am impressed with the syntactic elegance of the mechanism) but how it is used to avoid adding other features.

A phone with a touchscreen is evolutionary; a phone without a keypad is revolutionary. The revolution is in the unique experience of using "just comptime" for many things.

It is, of course, a tradeoff, and whether or not that tradeoff is "good" remains to be seen, but I think this design is one of the most novel designs in programming languages in many, many years.