Generic consts

Not to be confused with const generics, but I'll use both to describe the idea.

Let's say you have a const initializer and you want it to be different for every type:

const NONE_T_8ARRAY<T>: [Option<T>; 8] = [None; 8];

This is the basic generic const construct. Ofc, if you want length also specified:

const NONE_T_ARRAY<T, const L: usize>: [Option<T>; L] = [None; L];

This creates an array of size L containing only None.

Ofc, you also don't need to use types, consts are fine too:

const SQUARE<const X: usize>: usize = X * X;

But perhaps you want it to be recursive:

const POW<const X: usize, 0>: usize = 1;
const POW<const X: usize, const Y: usize>: usize = X * POW<X, Y-1>;

And you want to calculate Pi with it [1]:

const POW<const X: usize, 0>: usize = 1;
const POW<const X: usize, const Y: usize>: usize = X * POW<X, Y-1>;
const PI<-1>: f64 = 0;
const PI<const N: isize>: f64 = (1.0/POW<16, N as usize> * (4.0/(8*N + 1.0) - 2.0/(8*N + 4.0) - 1.0/(8*N + 5.0) - 1.0/(8*N + 6.0))) + PI<N-1>;

And things of the sort.

Yeah... they'd be nice.

May we have them?

Start by reviewing the proposed generic const examples and the linked C++ template-metaprogramming reference. The issue does not identify files, tests, an implementation entry point, or agreed acceptance criteria; the work would first need a concrete RFC design and a clear definition of what support is complete.