# Trait core::cmp::Ord

1.0.0 · source · [−]

    pub trait Ord: Eq + PartialOrd<Self> {
        fn cmp(&self, other: &Self) -> Ordering;

        fn max(self, other: Self) -> Self
        where
            Self: Sized,
        { ... }
        fn min(self, other: Self) -> Self
        where
            Self: Sized,
        { ... }
        fn clamp(self, min: Self, max: Self) -> Self
        where
            Self: Sized,
            Self: PartialOrd,
        { ... }
    }

Expand description

Trait for types that form a total order.

Implementations must be consistent with the `PartialOrd` implementation, and ensure `max`, `min`, and `clamp` are consistent with `cmp`:

- `partial_cmp(a, b) == Some(cmp(a, b))`.
- `max(a, b) == max_by(a, b, cmp)` (ensured by the default implementation).
- `min(a, b) == min_by(a, b, cmp)` (ensured by the default implementation).
- For `a.clamp(min, max)`, see the method docs (ensured by the default implementation).

It’s easy to accidentally make `cmp` and `partial_cmp` disagree by deriving some of the traits and manually implementing others.

### Corollaries

From the above and the requirements of `PartialOrd`, it follows that `<` defines a strict total order. This means that for all `a`, `b` and `c`:

- exactly one of `a < b`, `a == b` or `a > b` is true; and
- `<` is transitive: `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.

### Derivable

This trait can be used with `#[derive]`.

When `derive`d on structs, it will produce a lexicographic ordering based on the top-to-bottom declaration order of the struct’s members.

When `derive`d on enums, variants are ordered by their discriminants. By default, the discriminant is smallest for variants at the top, and largest for variants at the bottom. Here’s an example:

    #[derive(PartialEq, Eq, PartialOrd, Ord)]
    enum E {
        Top,
        Bottom,
    }

    assert!(E::Top < E::Bottom);

Run

However, manually setting the discriminants can override this default behavior:

    #[derive(PartialEq, Eq, PartialOrd, Ord)]
    enum E {
        Top = 2,
        Bottom = 1,
    }

    assert!(E::Bottom < E::Top);

Run

### Lexicographical comparison

Lexicographical comparison is an operation with the following properties:

- Two sequences are compared element by element.
- The first mismatching element defines which sequence is lexicographically less or greater than the other.
- If one sequence is a prefix of another, the shorter sequence is lexicographically less than the other.
- If two sequence have equivalent elements and are of the same length, then the sequences are lexicographically equal.
- An empty sequence is lexicographically less than any non-empty sequence.
- Two empty sequences are lexicographically equal.

### How can I implement `Ord`?

`Ord` requires that the type also be `PartialOrd` and `Eq` (which requires `PartialEq`).

Then you must define an implementation for `cmp`. You may find it useful to use `cmp` on your type’s fields.

Here’s an example where you want to sort people by height only, disregarding `id` and `name`:

    use std::cmp::Ordering;

    #[derive(Eq)]
    struct Person {
        id: u32,
        name: String,
        height: u32,
    }

    impl Ord for Person {
        fn cmp(&self, other: &Self) -> Ordering {
            self.height.cmp(&other.height)
        }
    }

    impl PartialOrd for Person {
        fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
            Some(self.cmp(other))
        }
    }

    impl PartialEq for Person {
        fn eq(&self, other: &Self) -> bool {
            self.height == other.height
        }
    }

Run

## Required Methods

source

#### fn cmp(&self, other: &Self) -> Ordering

This method returns an `Ordering` between `self` and `other`.

By convention, `self.cmp(&other)` returns the ordering matching the expression `self <operator> other` if true.

##### Examples

    use std::cmp::Ordering;

    assert_eq!(5.cmp(&10), Ordering::Less);
    assert_eq!(10.cmp(&5), Ordering::Greater);
    assert_eq!(5.cmp(&5), Ordering::Equal);

Run

## Provided Methods

1.21.0 · source

#### fn max(self, other: Self) -> Selfwhere
Self: Sized,

Compares and returns the maximum of two values.

Returns the second argument if the comparison determines them to be equal.

##### Examples

    assert_eq!(2, 1.max(2));
    assert_eq!(2, 2.max(2));

Run
1.21.0 · source

#### fn min(self, other: Self) -> Selfwhere
Self: Sized,

Compares and returns the minimum of two values.

Returns the first argument if the comparison determines them to be equal.

##### Examples

    assert_eq!(1, 1.min(2));
    assert_eq!(2, 2.min(2));

Run
1.50.0 · source

#### fn clamp(self, min: Self, max: Self) -> Selfwhere
Self: Sized,
Self: PartialOrd,

Restrict a value to a certain interval.

Returns `max` if `self` is greater than `max`, and `min` if `self` is less than `min`. Otherwise this returns `self`.

##### Panics

Panics if `min > max`.

##### Examples

    assert!((-3).clamp(-2, 1) == -2);
    assert!(0.clamp(-2, 1) == 0);
    assert!(2.clamp(-2, 1) == 1);

Run

## Implementors

1.34.0 · source

### impl Ord for Infallible

source

### impl Ord for Which

const: unstable · source

### impl Ord for Ordering

const: unstable · source

### impl Ord for bool

const: unstable · source

### impl Ord for char

const: unstable · source

### impl Ord for i8

const: unstable · source

### impl Ord for i16

const: unstable · source

### impl Ord for i32

const: unstable · source

### impl Ord for i64

const: unstable · source

### impl Ord for i128

const: unstable · source

### impl Ord for isize

const: unstable · source

### impl Ord for !

source

### impl Ord for str

Implements ordering of strings.

Strings are ordered lexicographically by their byte values. This orders Unicode code points based on their positions in the code charts. This is not necessarily the same as “alphabetical” order, which varies by language and locale. Sorting strings according to culturally-accepted standards requires locale-specific data that is outside the scope of the `str` type.

const: unstable · source

### impl Ord for u8

const: unstable · source

### impl Ord for u16

const: unstable · source

### impl Ord for u32

const: unstable · source

### impl Ord for u64

const: unstable · source

### impl Ord for u128

const: unstable · source

### impl Ord for ()

const: unstable · source

### impl Ord for usize

source

### impl Ord for TypeId

1.27.0 · source

### impl Ord for CpuidResult

Available on x86 or x86-64 only.
source

### impl Ord for CStr

source

### impl Ord for Error

1.33.0 · source

### impl Ord for PhantomPinned

1.34.0 · source

### impl Ord for NonZeroI8

1.34.0 · source

### impl Ord for NonZeroI16

1.34.0 · source

### impl Ord for NonZeroI32

1.34.0 · source

### impl Ord for NonZeroI64

1.34.0 · source

### impl Ord for NonZeroI128

1.34.0 · source

### impl Ord for NonZeroIsize

1.28.0 · source

### impl Ord for NonZeroU8

1.28.0 · source

### impl Ord for NonZeroU16

1.28.0 · source

### impl Ord for NonZeroU32

1.28.0 · source

### impl Ord for NonZeroU64

1.28.0 · source

### impl Ord for NonZeroU128

1.28.0 · source

### impl Ord for NonZeroUsize

source

### impl Ord for Alignment

1.3.0 · source

### impl Ord for Duration

1.10.0 · source

### impl<'a> Ord for Location<'a>

source

### impl<A: ?Sized> Ord for &Awhere
A: Ord,

source

### impl<A: ?Sized> Ord for &mut Awhere
A: Ord,

source

### impl<Dyn: ?Sized> Ord for DynMetadata<Dyn>

1.41.0 · source

### impl<P: Deref<Target: Ord>> Ord for Pin<P>

1.4.0 · source

### impl<Ret, T> Ord for fn (T₁, T₂, …, Tₙ) -> Ret

This trait is implemented for function pointers with up to twelve arguments.

1.4.0 · source

### impl<Ret, T> Ord for extern "C" fn (T₁, T₂, …, Tₙ) -> Ret

This trait is implemented for function pointers with up to twelve arguments.

1.4.0 · source

### impl<Ret, T> Ord for extern "C" fn (T₁, T₂, …, Tₙ, ...) -> Ret

This trait is implemented for function pointers with up to twelve arguments.

source

### impl<Ret, T> Ord for extern "C-unwind" fn (T₁, T₂, …, Tₙ) -> Ret

This trait is implemented for function pointers with up to twelve arguments.

source

### impl<Ret, T> Ord for extern "C-unwind" fn (T₁, T₂, …, Tₙ, ...) -> Ret

This trait is implemented for function pointers with up to twelve arguments.

1.4.0 · source

### impl<Ret, T> Ord for unsafe fn (T₁, T₂, …, Tₙ) -> Ret

This trait is implemented for function pointers with up to twelve arguments.

1.4.0 · source

### impl<Ret, T> Ord for unsafe extern "C" fn (T₁, T₂, …, Tₙ) -> Ret

This trait is implemented for function pointers with up to twelve arguments.

1.4.0 · source

### impl<Ret, T> Ord for unsafe extern "C" fn (T₁, T₂, …, Tₙ, ...) -> Ret

This trait is implemented for function pointers with up to twelve arguments.

source

### impl<Ret, T> Ord for unsafe extern "C-unwind" fn (T₁, T₂, …, Tₙ) -> Ret

This trait is implemented for function pointers with up to twelve arguments.

source

### impl<Ret, T> Ord for unsafe extern "C-unwind" fn (T₁, T₂, …, Tₙ, ...) -> Ret

This trait is implemented for function pointers with up to twelve arguments.

source

### impl<T, const LANES: usize> Ord for Simd<T, LANES>where
LaneCount<LANES>: SupportedLaneCount,
T: SimdElement + Ord,

1.10.0 · source

### impl<T: Ord + Copy> Ord for Cell<T>

1.20.0 · source

### impl<T: Ord + ?Sized> Ord for ManuallyDrop<T>

source

### impl<T: Ord> Ord for Option<T>

1.36.0 · source

### impl<T: Ord> Ord for Poll<T>

source

### impl<T: Ord> Ord for [T]

Implements comparison of vectors lexicographically.

source

### impl<T: Ord> Ord for (T₁, T₂, …, Tₙ)where
T: ?Sized,

This trait is implemented for tuples up to twelve items long.

source

### impl<T: Ord> Ord for Saturating<T>

source

### impl<T: Ord> Ord for Wrapping<T>

1.19.0 · source

### impl<T: Ord> Ord for Reverse<T>

source

### impl<T: Ord, E: Ord> Ord for Result<T, E>

source

### impl<T: Ord, const N: usize> Ord for [T; N]

Implements comparison of arrays lexicographically.

1.10.0 · source

### impl<T: ?Sized + Ord> Ord for RefCell<T>

source

### impl<T: ?Sized> Ord for *const T

source

### impl<T: ?Sized> Ord for *mut T

source

### impl<T: ?Sized> Ord for PhantomData<T>

1.25.0 · source

### impl<T: ?Sized> Ord for NonNull<T>

source

### impl<Y: Ord, R: Ord> Ord for GeneratorState<Y, R>