Crate enum_ordinalize

Expand description

Enum Ordinalize

This crates provides a procedural macro to let enums not only get its variants’ ordinal but also be constructed from an ordinal.

Use #[derive(Ordinalize)] to make an enum (which must only has unit variants) have from_ordinal_unsafe, from_ordinal, variants, and variant_count associated functions and a ordinal method.

#[macro_use] extern crate enum_ordinalize;

#[derive(Debug, PartialEq, Eq, Ordinalize)]
enum MyEnum {
    Zero,
    One,
    Two,
}

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) });

Get Variants

#[macro_use] extern crate enum_ordinalize;

#[derive(Debug, PartialEq, Eq, Ordinalize)]
enum MyEnum {
    Zero,
    One,
    Two,
}

assert_eq!([MyEnum::Zero, MyEnum::One, MyEnum::Two], MyEnum::variants());
assert_eq!(3, MyEnum::variant_count());

variants and variant_count are constant functions.

The (Ordinal) Size of an Enum

The ordinal value is an integer whose size is determined by the enum itself. The larger (or the smaller if it’s negative) the variants’ values are, the bigger the enum size is.

For example,

#[macro_use] extern crate enum_ordinalize;

#[derive(Debug, PartialEq, Eq, Ordinalize)]
enum MyEnum {
    Zero,
    One,
    Two,
    Thousand = 1000,
}

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 store 1000, the size of MyEnum grows. Thus, the ordinal is in i16 instead of i8.

You can use the #[repr(type)] attribute to control the size explicitly. For instance,

#[macro_use] extern crate enum_ordinalize;

#[derive(Debug, PartialEq, Eq, Ordinalize)]
#[repr(usize)]
enum MyEnum {
    Zero,
    One,
    Two,
    Thousand = 1000,
}

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 are extended in successive increments and can be set explicitly from anywhere.

#[macro_use] extern crate enum_ordinalize;

#[derive(Debug, PartialEq, Eq, Ordinalize)]
enum MyEnum {
    Two   = 2,
    Three,
    Four,
    Eight = 8,
    Nine,
    NegativeTen = -10,
    NegativeNine,
}

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) });

Derive Macros

Ordinalize