How do I format a signed integer to a sign-aware hexadecimal representation?

Question

My initial intent was to convert a signed primitive number to its hexadecimal representation in a way that preserves the number\'s sign. It turns out that the current implem

Answer 1

This is like Francis Gagné's answer, but made generic to handle i8 through i128.

use std::fmt::{self, Formatter, UpperHex};
use num_traits::Signed;

struct ReallySigned(T);

impl UpperHex for ReallySigned {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        let prefix = if f.alternate() { "0x" } else { "" };
        let bare_hex = format!("{:X}", self.0.abs());
        f.pad_integral(self.0 >= T::zero(), prefix, &bare_hex)
    }
}

fn main() {
    println!("{:#X}", -0x12345678);
    println!("{:#X}", ReallySigned(-0x12345678));
}