ConstDefault Trait

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]
const-default = { version = "1.0", features = ["derive"] }

to your Cargo.toml to start using it.

Examples

Rust Primitives

use const_default::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 const_default::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(),
    );
}