Format numbers in constant expressions

help
1

Is it possible to format numbers (integer, in practice) in constant expressions? Like the example below:

struct MyNumber(i32);
impl MyNumber {
    const fn format_self(&self) -> &'static str {
        const_formatter::format(self.0)
    }
}

I've tried the "const_format" and "const_str" crate, but both of them use const value in their internal implementation. Is there any other workaround?

2

The problem is that a const fn is not always constant, it is supposed to be callable at runtime too. And you can't get a &'static str representing a runtime value (unless you e.g. leak memory, but that's generally unwanted).

3

I haven't found one yet (though string concatenation isn't exactly the same type of operation as number formatting, so maybe you'll have more luck than me).

4

What if my function only needs to be called during compile time?

Maybe a macro system could do it, but I don't want to try to implement complex operations within macro. :frowning:

Edit:

I'm trying to implement this with macros. Never wanted postfix macro to be stable so much.

5

Does this suit your needs? https://docs.rs/const_format/latest/const_format/

6

My last solution was to wrap this in a macro, since only macros can be used to ensure const-only use. Anyway, thanks for the advice!