More robust and versatile implementation of derive(Debug) and derive(Display). Unlike the version ofderive(Debug) in the standard library, these macros will always successfully generate an implementation - even if a member does not implement Debug/Display. In that case, the generated implementation will print a replacement string of the form <TypeName>.

use fmt_derive::Debug; // replacement for `use std::fmt::Debug;`

// a type that implements neither `Debug` nor `Display`
struct Unprintable;

#[derive(Debug, crate::Display)]
struct Printable {
	// unprintable members will be printed as `<Type>`
	unprintable: Unprintable,

	// use `#[display(ignore)]` (or `#[debug(ignore]` respectively) to skip a member when printing
	#[display(ignore)]
	ignored: u32,

	// use the `fmt` attribute to refer to both `Debug` and `Display` at once
	#[fmt("{:#08X}", self.hex_number)]
	hex_number: u32,
}

fn main() {
	let printable = Printable{
		hex_number: 0xDEADBEEF,
		ignored: 42,
		unprintable: Unprintable,
	};

	assert_eq!(format!("{:?}", printable), "Printable { unprintable: <Unprintable>, ignored: 42, hex_number: 0xDEADBEEF }");
	assert_eq!(format!("{}", printable), "Printable { unprintable: <Unprintable>, hex_number: 0xDEADBEEF }");
}

no_std

This crate is no_std and can be used from both no_std and std contexts without any action required.

MSRV

The current MSRV is 1.56.0.

TODO

• The format expressions on enumeration variants and fields show that this crate will probably need a better method of referring to fields (currently, self is accessible, which requires unwrapping the variant each time it is used)