Trait Ordinal

Source

pub trait Ordinal: Sized {
    const ORDINAL_SIZE: usize;

    // Required methods
    fn ordinal(&self) -> usize;
    fn from_ordinal(ordinal: usize) -> Option<Self>;

    // Provided method
    fn all_values() -> OrdinalValues<Self> ⓘ { ... }
}

Expand description

Two-way map from a type to usize range from 0..ORDINAL_SIZE.

Two way ordinal mapping means:

the type has ORDINAL_SIZE possible values
each value has a unique ordinal number in the range 0..ORDINAL_SIZE
each ordinal number corresponds to a unique value

This type is implemented for

small integer types
tuples
some builtin types like Option and Result
and it can be derived with the #[derive(Ordinal)] attribute for structs and enums

§Relation to `Ord` and `PartialOrd`

Implementations provided in this crate and generated with #[derive(Ordinal)] are compatible with Ord and PartialOrd, meaning a < b <=> a.ordinal() < b.ordinal() with the exception of derive on enums with explicit discriminants (derive ignores them and assigns ordinal numbers in order of declaration).

This is not enforced by the trait itself, but it is a good practice to follow.

§Derive

#[derive(Ordinal)] works for arbitrary structs and enums. Generated implementation is compatible with #[derive(PartialOrd)].

use ordinal_map::Ordinal;
#[derive(Ordinal)]
enum Color {
    Red,
    Cyan,
    Blue,
}

#[derive(Ordinal)]
struct Bright(bool);

#[derive(Ordinal)]
enum MaybeColor {
    Default,
    Colored(Color, Bright),
    Invisible,
}

assert_eq!(0, MaybeColor::Default.ordinal());
assert_eq!(1, MaybeColor::Colored(Color::Red, Bright(false)).ordinal());
assert_eq!(2, MaybeColor::Colored(Color::Red, Bright(true)).ordinal());
assert_eq!(3, MaybeColor::Colored(Color::Cyan, Bright(false)).ordinal());
assert_eq!(4, MaybeColor::Colored(Color::Cyan, Bright(true)).ordinal());

§See also

Iter to iterate over all possible values.
map module for constant time lookup maps.
set module for constant time lookup sets.

Required Associated Constants§

Source

const ORDINAL_SIZE: usize

Number of possible values.

It is compile-time error if the number of possible values is greater than usize::MAX.

Required Methods§

Source

fn ordinal(&self) -> usize

Index of the ordinal.

§Example

use std::num::NonZeroI16;

use ordinal_map::Ordinal;
assert_eq!(0, None::<u16>.ordinal());
assert_eq!(1, Some::<u16>(0).ordinal());
assert_eq!(2, Some::<u16>(1).ordinal());

Source

fn from_ordinal(ordinal: usize) -> Option<Self>

Returns the ordinal from the index.

§Example

use ordinal_map::Ordinal;

assert_eq!(i16::MIN, i16::from_ordinal(0).unwrap());
assert_eq!(i16::MIN + 1, i16::from_ordinal(1).unwrap());

Provided Methods§

Source

fn all_values() -> OrdinalValues<Self> ⓘ

Iterate over all possible values.

Values are returned in order of their ordinal numbers.

§Example

use ordinal_map::Ordinal;
let mut iter = i16::all_values();
assert_eq!(Some(i16::MIN), iter.next());
assert_eq!(Some(i16::MAX), iter.next_back());

Dyn Compatibility§

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Trait Ordinal Copy item path

§Relation to Ord and PartialOrd

§Derive

§See also

Required Associated Constants§

const ORDINAL_SIZE: usize

Required Methods§

fn ordinal(&self) -> usize

§Example

fn from_ordinal(ordinal: usize) -> Option<Self>

§Example

Provided Methods§

fn all_values() -> OrdinalValues<Self> ⓘ

§Example

Dyn Compatibility§

Implementations on Foreign Types§

impl Ordinal for ()

const ORDINAL_SIZE: usize = 1usize

fn ordinal(&self) -> usize

fn from_ordinal(ordinal: usize) -> Option<Self>

impl Ordinal for Infallible

const ORDINAL_SIZE: usize = 0

fn ordinal(&self) -> usize

fn from_ordinal(_: usize) -> Option<Self>

impl Ordinal for NonZeroI8

const ORDINAL_SIZE: usize = NonZeroU8::ORDINAL_SIZE

fn ordinal(&self) -> usize

fn from_ordinal(ordinal: usize) -> Option<Self>

impl Ordinal for NonZeroI16

const ORDINAL_SIZE: usize = NonZeroU16::ORDINAL_SIZE

fn ordinal(&self) -> usize

fn from_ordinal(ordinal: usize) -> Option<Self>

impl Ordinal for NonZeroI32

const ORDINAL_SIZE: usize = NonZeroU32::ORDINAL_SIZE

fn ordinal(&self) -> usize

fn from_ordinal(ordinal: usize) -> Option<Self>

impl Ordinal for NonZeroI64

const ORDINAL_SIZE: usize = NonZeroU64::ORDINAL_SIZE

fn ordinal(&self) -> usize

fn from_ordinal(ordinal: usize) -> Option<Self>

impl Ordinal for NonZeroIsize

const ORDINAL_SIZE: usize = NonZeroUsize::ORDINAL_SIZE

fn ordinal(&self) -> usize

fn from_ordinal(ordinal: usize) -> Option<Self>

impl Ordinal for NonZeroU8

const ORDINAL_SIZE: usize

fn ordinal(&self) -> usize

fn from_ordinal(ordinal: usize) -> Option<Self>

impl Ordinal for NonZeroU16

const ORDINAL_SIZE: usize

fn ordinal(&self) -> usize

fn from_ordinal(ordinal: usize) -> Option<Self>

impl Ordinal for NonZeroU32

const ORDINAL_SIZE: usize

fn ordinal(&self) -> usize

fn from_ordinal(ordinal: usize) -> Option<Self>

impl Ordinal for NonZeroU64

const ORDINAL_SIZE: usize

fn ordinal(&self) -> usize

fn from_ordinal(ordinal: usize) -> Option<Self>

impl Ordinal for NonZeroUsize

const ORDINAL_SIZE: usize = usize::MAX

fn ordinal(&self) -> usize

fn from_ordinal(ordinal: usize) -> Option<Self>

impl Ordinal for Ordering

const ORDINAL_SIZE: usize = 3

fn ordinal(&self) -> usize

fn from_ordinal(ordinal: usize) -> Option<Self>

impl Ordinal for bool

const ORDINAL_SIZE: usize = 2

fn ordinal(&self) -> usize

fn from_ordinal(ordinal: usize) -> Option<Self>

impl Ordinal for char

const ORDINAL_SIZE: usize

fn ordinal(&self) -> usize

fn from_ordinal(ordinal: usize) -> Option<Self>

impl Ordinal for i8

const ORDINAL_SIZE: usize

fn ordinal(&self) -> usize

fn from_ordinal(ordinal: usize) -> Option<Self>

Trait Ordinal

§Relation to `Ord` and `PartialOrd`