Crate display_with

A simple crate that provides a way to create instances of opaque types that implement fmt::Display and fmt::Debug by calling a provided formatting closure.

Examples

use display_with::{display_with, debug_with};

let display = display_with(|f| write!(f, "Hello, world!"));
assert_eq!(format!("{display}"), "Hello, world!");

let debug = debug_with(|f| write!(f, "Hello, world!"));
assert_eq!(format!("{debug:?}"), "Hello, world!");

This can be combined with the format_args! macro to use the opaque types with the write! and writeln! macros.

use core::fmt::Write;
use display_with::{display_with, debug_with};

fn main() -> std::fmt::Result {
    let display = display_with(|f| write!(f, "Hello, world!"));
    let mut s = String::new();
    // Unlike `s.push_str(&format!("{display}"))`, this doesn't require an extra allocation.
    write!(&mut s, "{}", format_args!("{display}"))?;
    Ok(())
}

Credit: https://internals.rust-lang.org/t/format-args-with-long-lifetimes/19494/2.

Functions

debug_with

Creates an instance of an opaque type that implements fmt::Debug by calling the provided formatting closure.

display_with

Creates an instance of an opaque type that implements fmt::Display by calling the provided formatting closure.