Named Constants

Procedural macro makes enums behave like named constants in languages like C/C++ or C#.

Put this attribute on an enum and it will be rewritten as a newtype struct. The enum variants are turned into associated constants.

Examples

use named_constants::named_constants;

#[named_constants]
// Derives are applied to the newtype wrapper
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
// Required repr to specify the underlying type
#[repr(i32)]
pub enum CardSuit {
	CLUBS,      // (= 0) Starts from zero
	DIAMONDS,   // (= 1) Autoincrements the previous value
	HEARTS = 4, // (= 4) Direct assignment
	SPADES,     // (= 5) Autoincrements the previous value
}

let clubs = CardSuit::CLUBS;
let weird = CardSuit(14); // Legal!

Implementation notes

In the example above, CardSuit is transformed into:

#[derive(Copy, Clone, Debug, Eq, PartialEq)]
#[repr(transparent)]
pub struct CardSuit(pub i32);
impl CardSuit {
	pub const CLUBS: CardSuit = CardSuit(0);
	pub const DIAMONDS: CardSuit = CardSuit(1);
	pub const HEARTS: CardSuit = CardSuit(4);
	pub const SPADES: CardSuit = CardSuit(4 + 1);
}

License

Licensed under MIT License, see license.txt.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, shall be licensed as above, without any additional terms or conditions.