2 unstable releases
0.2.0 | Nov 12, 2022 |
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0.1.0 | Oct 13, 2020 |
#2132 in Rust patterns
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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.