TypeFunction example creatiing a conversion matrix

[jmh530]

On Thursday, 1 October 2020 at 09:54:25 UTC, Stefan Koch wrote:
> [snip]
>
> I mean on the other hand.
> Maybe I should be motivated.
> Now I can do a direct comparison to alternative implementations.
> Without having to write the alternative myself.

I certainly think it's interesting and seems more straightforward 
than Andrei's reification example, but more concrete results will 
help your case. You might make a few examples of both simple and 
complex use cases of this technique and compare (at least 
compile-time and the size of object files) to the current D 
compiler and Andrei's reification approach. You might have a case 
if you can show quantitative improvements over the alternatives.

One thing that keeps coming to my mind when you are providing 
examples is the zig language's comptime [1]. They have the 
example of

fn max(comptime T: type, a: T, b: T) T {
     return if (a > b) a else b;
}
fn gimmeTheBiggerFloat(a: f32, b: f32) f32 {
     return max(f32, a, b);
}
fn gimmeTheBiggerInteger(a: u64, b: u64) u64 {
     return max(u64, a, b);
}

and obviously this could be done in D with templates. But if type 
functions were in D, then I would imagine you should also be able 
to do it like:

T max(alias T, T a, T b) {
     return (a > b) ? a : b;
}
float gimmeTheBiggerFloat(float a, float b) {
     return max(float, a, b);
}
uint gimmeTheBiggerInteger(uint a, uint b) {
     return max(uint, a, b);
}


[1] 
https://ziglang.org/documentation/master/#Introducing-the-Compile-Time-Concept