macro constdefault-derive

#[derive(ConstDefault)]

2 releases

0.2.1 Sep 27, 2022
0.2.0 Sep 27, 2022


Used in constdefault

MIT license

8KB
71 lines

ConstDefault Trait

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A Default-like trait and derive macros for const evaluation contexts.

This crate defines the ConstDefault trait and implements it for Rust primitives, prelude types, tuples and arrays. Furthermore it provides a derive macro so that users can implement ConstDefault easily for their custom types.

  • 100% safe Rust
  • no_std compatible
  • Full macro hygiene
  • No dependencies

Usage

Add

[dependencies]
constdefault = { version = "1.0", features = ["derive"] }

to your Cargo.toml to start using it.

Examples

Rust Primitives

use constdefault::ConstDefault;

fn main() {
    assert_eq!(<i32 as ConstDefault>::DEFAULT, 0);
    assert_eq!(<Option<i32> as ConstDefault>::DEFAULT, None);
    assert_eq!(<String as ConstDefault>::DEFAULT, String::new());
    assert_eq!(<Vec<u8> as ConstDefault>::DEFAULT, Vec::new());
}

Derive

use constdefault::ConstDefault;

#[derive(ConstDefault, Debug, Default, PartialEq)]
pub struct Color {
    r: u8,
    g: u8,
    b: u8,
}

fn main() {
    assert_eq!(
        <Color as ConstDefault>::DEFAULT,
        Color::default(),
    );
}

Dependencies

~1.5MB
~37K SLoC