Enum Ordinalize
This library enables enums to not only obtain the ordinal values of their variants but also allows for the construction of enums from an ordinal value.
Usage
Use #[derive(Ordinalize)]
to have an enum (which must only has unit variants) implement the Ordinalize
trait.
use enum_ordinalize::Ordinalize;
#[derive(Debug, PartialEq, Eq, Ordinalize)]
enum MyEnum {
Zero,
One,
Two,
}
assert_eq!(3, MyEnum::VARIANT_COUNT);
assert_eq!([MyEnum::Zero, MyEnum::One, MyEnum::Two], MyEnum::VARIANTS);
assert_eq!([0i8, 1i8, 2i8], MyEnum::VALUES);
assert_eq!(0i8, MyEnum::Zero.ordinal());
assert_eq!(1i8, MyEnum::One.ordinal());
assert_eq!(2i8, MyEnum::Two.ordinal());
assert_eq!(Some(MyEnum::Zero), MyEnum::from_ordinal(0i8));
assert_eq!(Some(MyEnum::One), MyEnum::from_ordinal(1i8));
assert_eq!(Some(MyEnum::Two), MyEnum::from_ordinal(2i8));
assert_eq!(MyEnum::Zero, unsafe { MyEnum::from_ordinal_unsafe(0i8) });
assert_eq!(MyEnum::One, unsafe { MyEnum::from_ordinal_unsafe(1i8) });
assert_eq!(MyEnum::Two, unsafe { MyEnum::from_ordinal_unsafe(2i8) });
The (Ordinal) Size of an Enum
The ordinal value is an integer whose size is determined by the enum itself. The size of the enum increases with the magnitude of the variants' values, whether larger (or smaller if negative).
For example,
use enum_ordinalize::Ordinalize;
#[derive(Debug, PartialEq, Eq, Ordinalize)]
enum MyEnum {
Zero,
One,
Two,
Thousand = 1000,
}
assert_eq!(4, MyEnum::VARIANT_COUNT);
assert_eq!([MyEnum::Zero, MyEnum::One, MyEnum::Two, MyEnum::Thousand], MyEnum::VARIANTS);
assert_eq!([0i16, 1i16, 2i16, 1000i16], MyEnum::VALUES);
assert_eq!(0i16, MyEnum::Zero.ordinal());
assert_eq!(1i16, MyEnum::One.ordinal());
assert_eq!(2i16, MyEnum::Two.ordinal());
assert_eq!(Some(MyEnum::Zero), MyEnum::from_ordinal(0i16));
assert_eq!(Some(MyEnum::One), MyEnum::from_ordinal(1i16));
assert_eq!(Some(MyEnum::Two), MyEnum::from_ordinal(2i16));
assert_eq!(MyEnum::Zero, unsafe { MyEnum::from_ordinal_unsafe(0i16) });
assert_eq!(MyEnum::One, unsafe { MyEnum::from_ordinal_unsafe(1i16) });
assert_eq!(MyEnum::Two, unsafe { MyEnum::from_ordinal_unsafe(2i16) });
In order to accommodate the value 1000
, the size of MyEnum
increases. Consequently, the ordinal is represented in i16
instead of i8
.
You can utilize the #[repr(type)]
attribute to explicitly control the size. For instance,
use enum_ordinalize::Ordinalize;
#[derive(Debug, PartialEq, Eq, Ordinalize)]
#[repr(usize)]
enum MyEnum {
Zero,
One,
Two,
Thousand = 1000,
}
assert_eq!(4, MyEnum::VARIANT_COUNT);
assert_eq!([MyEnum::Zero, MyEnum::One, MyEnum::Two, MyEnum::Thousand], MyEnum::VARIANTS);
assert_eq!([0usize, 1usize, 2usize, 1000usize], MyEnum::VALUES);
assert_eq!(0usize, MyEnum::Zero.ordinal());
assert_eq!(1usize, MyEnum::One.ordinal());
assert_eq!(2usize, MyEnum::Two.ordinal());
assert_eq!(Some(MyEnum::Zero), MyEnum::from_ordinal(0usize));
assert_eq!(Some(MyEnum::One), MyEnum::from_ordinal(1usize));
assert_eq!(Some(MyEnum::Two), MyEnum::from_ordinal(2usize));
assert_eq!(MyEnum::Zero, unsafe { MyEnum::from_ordinal_unsafe(0usize) });
assert_eq!(MyEnum::One, unsafe { MyEnum::from_ordinal_unsafe(1usize) });
assert_eq!(MyEnum::Two, unsafe { MyEnum::from_ordinal_unsafe(2usize) });
Useful Increment
The integers represented by variants can be extended in successive increments and set explicitly from any value.
use enum_ordinalize::Ordinalize;
#[derive(Debug, PartialEq, Eq, Ordinalize)]
enum MyEnum {
Two = 2,
Three,
Four,
Eight = 8,
Nine,
NegativeTen = -10,
NegativeNine,
}
assert_eq!(7, MyEnum::VARIANT_COUNT);
assert_eq!([MyEnum::Two, MyEnum::Three, MyEnum::Four, MyEnum::Eight, MyEnum::Nine, MyEnum::NegativeTen, MyEnum::NegativeNine], MyEnum::VARIANTS);
assert_eq!([2i8, 3i8, 4i8, 8i8, 9i8, -10i8, -9i8], MyEnum::VALUES);
assert_eq!(4i8, MyEnum::Four.ordinal());
assert_eq!(9i8, MyEnum::Nine.ordinal());
assert_eq!(-9i8, MyEnum::NegativeNine.ordinal());
assert_eq!(Some(MyEnum::Four), MyEnum::from_ordinal(4i8));
assert_eq!(Some(MyEnum::Nine), MyEnum::from_ordinal(9i8));
assert_eq!(Some(MyEnum::NegativeNine), MyEnum::from_ordinal(-9i8));
assert_eq!(MyEnum::Four, unsafe { MyEnum::from_ordinal_unsafe(4i8) });
assert_eq!(MyEnum::Nine, unsafe { MyEnum::from_ordinal_unsafe(9i8) });
assert_eq!(MyEnum::NegativeNine, unsafe { MyEnum::from_ordinal_unsafe(-9i8) });
Crates.io
https://crates.io/crates/enum-ordinalize
Documentation
https://docs.rs/enum-ordinalize
License
MIT