"Hey Nim, 2014 called... they want their language features back."

I jest.

But seriously, D, Rust, and C++14 are about as familiar to me as Nim.

To be fair, D has had it since 2007 :)

Rust is planning to add that eventually, but in the meantime:

    fn foo(n: i32) -> i32 {
        n * 2
    }
    const y: i32 = foo(3);

error: function calls in constants are limited to struct and enum constructors [E0015]

You can do it with a compiler plugin; I suspect that's what the parent comment was referring to. Admittedly compiler plugins are pretty experimental at this time.

Sorry about that. I haven't tried this myself, I was told by a Rust user that its CTFE was on par with D's. I guess he was mistaken.

Not even close, sadly.

Or Common Lisp, 30 years ago.