Ordering in std::cmp - Rust
Description: An `Ordering` is the result of a comparison between two values.

## Ordering

# Enum Ordering

1.0.0 · Source

    #[repr(i8)]pub enum Ordering {
        Less = -1,
        Equal = 0,
        Greater = 1,
    }

Expand description

An `Ordering` is the result of a comparison between two values.

## §Examples

    use std::cmp::Ordering;

    assert_eq!(1.cmp(&2), Ordering::Less);

    assert_eq!(1.cmp(&1), Ordering::Equal);

    assert_eq!(2.cmp(&1), Ordering::Greater);

## Variants§

§1.0.0

### Less = -1

An ordering where a compared value is less than another.

§1.0.0

### Equal = 0

An ordering where a compared value is equal to another.

§1.0.0

### Greater = 1

An ordering where a compared value is greater than another.

## Implementations§

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### impl Ordering

1.53.0 (const: 1.53.0) · Source

#### pub const fn is_eq(self) -> bool

Returns `true` if the ordering is the `Equal` variant.

##### §Examples

    use std::cmp::Ordering;

    assert_eq!(Ordering::Less.is_eq(), false);
    assert_eq!(Ordering::Equal.is_eq(), true);
    assert_eq!(Ordering::Greater.is_eq(), false);

1.53.0 (const: 1.53.0) · Source

#### pub const fn is_ne(self) -> bool

Returns `true` if the ordering is not the `Equal` variant.

##### §Examples

    use std::cmp::Ordering;

    assert_eq!(Ordering::Less.is_ne(), true);
    assert_eq!(Ordering::Equal.is_ne(), false);
    assert_eq!(Ordering::Greater.is_ne(), true);

1.53.0 (const: 1.53.0) · Source

#### pub const fn is_lt(self) -> bool

Returns `true` if the ordering is the `Less` variant.

##### §Examples

    use std::cmp::Ordering;

    assert_eq!(Ordering::Less.is_lt(), true);
    assert_eq!(Ordering::Equal.is_lt(), false);
    assert_eq!(Ordering::Greater.is_lt(), false);

1.53.0 (const: 1.53.0) · Source

#### pub const fn is_gt(self) -> bool

Returns `true` if the ordering is the `Greater` variant.

##### §Examples

    use std::cmp::Ordering;

    assert_eq!(Ordering::Less.is_gt(), false);
    assert_eq!(Ordering::Equal.is_gt(), false);
    assert_eq!(Ordering::Greater.is_gt(), true);

1.53.0 (const: 1.53.0) · Source

#### pub const fn is_le(self) -> bool

Returns `true` if the ordering is either the `Less` or `Equal` variant.

##### §Examples

    use std::cmp::Ordering;

    assert_eq!(Ordering::Less.is_le(), true);
    assert_eq!(Ordering::Equal.is_le(), true);
    assert_eq!(Ordering::Greater.is_le(), false);

1.53.0 (const: 1.53.0) · Source

#### pub const fn is_ge(self) -> bool

Returns `true` if the ordering is either the `Greater` or `Equal` variant.

##### §Examples

    use std::cmp::Ordering;

    assert_eq!(Ordering::Less.is_ge(), false);
    assert_eq!(Ordering::Equal.is_ge(), true);
    assert_eq!(Ordering::Greater.is_ge(), true);

1.0.0 (const: 1.48.0) · Source

#### pub const fn reverse(self) -> Ordering

Reverses the `Ordering`.

- `Less` becomes `Greater`.
- `Greater` becomes `Less`.
- `Equal` becomes `Equal`.

##### §Examples

Basic behavior:

    use std::cmp::Ordering;

    assert_eq!(Ordering::Less.reverse(), Ordering::Greater);
    assert_eq!(Ordering::Equal.reverse(), Ordering::Equal);
    assert_eq!(Ordering::Greater.reverse(), Ordering::Less);

This method can be used to reverse a comparison:

    let data: &mut [_] = &mut [2, 10, 5, 8];

    // sort the array from largest to smallest.
    data.sort_by(|a, b| a.cmp(b).reverse());

    let b: &mut [_] = &mut [10, 8, 5, 2];
    assert!(data == b);

1.17.0 (const: 1.48.0) · Source

#### pub const fn then(self, other: Ordering) -> Ordering

Chains two orderings.

Returns `self` when it’s not `Equal`. Otherwise returns `other`.

##### §Examples

    use std::cmp::Ordering;

    let result = Ordering::Equal.then(Ordering::Less);
    assert_eq!(result, Ordering::Less);

    let result = Ordering::Less.then(Ordering::Equal);
    assert_eq!(result, Ordering::Less);

    let result = Ordering::Less.then(Ordering::Greater);
    assert_eq!(result, Ordering::Less);

    let result = Ordering::Equal.then(Ordering::Equal);
    assert_eq!(result, Ordering::Equal);

    let x: (i64, i64, i64) = (1, 2, 7);
    let y: (i64, i64, i64) = (1, 5, 3);
    let result = x.0.cmp(&y.0).then(x.1.cmp(&y.1)).then(x.2.cmp(&y.2));

    assert_eq!(result, Ordering::Less);

1.17.0 (const: unstable) · Source

#### pub fn then_with<F>(self, f: F) -> Ordering
where F: FnOnce() -> Ordering,

Chains the ordering with the given function.

Returns `self` when it’s not `Equal`. Otherwise calls `f` and returns the result.

##### §Examples

    use std::cmp::Ordering;

    let result = Ordering::Equal.then_with(|| Ordering::Less);
    assert_eq!(result, Ordering::Less);

    let result = Ordering::Less.then_with(|| Ordering::Equal);
    assert_eq!(result, Ordering::Less);

    let result = Ordering::Less.then_with(|| Ordering::Greater);
    assert_eq!(result, Ordering::Less);

    let result = Ordering::Equal.then_with(|| Ordering::Equal);
    assert_eq!(result, Ordering::Equal);

    let x: (i64, i64, i64) = (1, 2, 7);
    let y: (i64, i64, i64) = (1, 5, 3);
    let result = x.0.cmp(&y.0).then_with(|| x.1.cmp(&y.1)).then_with(|| x.2.cmp(&y.2));

    assert_eq!(result, Ordering::Less);

## Trait Implementations§

1.0.0 (const: unstable) · Source§

### impl Clone for Ordering

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#### fn clone(&self) -> Ordering

Returns a duplicate of the value. Read more
1.0.0 · Source§

#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
1.0.0 · Source§

### impl Debug for Ordering

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#### fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter. Read more
1.0.0 · Source§

### impl Hash for Ordering

Source§

#### fn hash<__H>(&self, state: &mut __H)
where __H: Hasher,

Feeds this value into the given `Hasher`. Read more
1.3.0 · Source§

#### fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,

Feeds a slice of this type into the given `Hasher`. Read more
1.0.0 (const: unstable) · Source§

### impl Ord for Ordering

Source§

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

This method returns an `Ordering` between `self` and `other`. Read more
1.21.0 · Source§

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

Compares and returns the maximum of two values. Read more
1.21.0 · Source§

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

Compares and returns the minimum of two values. Read more
1.50.0 · Source§

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

Restrict a value to a certain interval. Read more
1.0.0 (const: unstable) · Source§

### impl PartialEq for Ordering

Source§

#### fn eq(&self, other: &Ordering) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 · Source§

#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 (const: unstable) · Source§

### impl PartialOrd for Ordering

Source§

#### fn partial_cmp(&self, other: &Ordering) -> Option<Ordering>

This method returns an ordering between `self` and `other` values if one exists. Read more
1.0.0 · Source§

#### fn lt(&self, other: &Rhs) -> bool

Tests less than (for `self` and `other`) and is used by the `<` operator. Read more
1.0.0 · Source§

#### fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
1.0.0 · Source§

#### fn gt(&self, other: &Rhs) -> bool

Tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
1.0.0 · Source§

#### fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
1.0.0 · Source§

### impl Copy for Ordering

1.0.0 (const: unstable) · Source§

### impl Eq for Ordering

1.0.0 · Source§

### impl StructuralPartialEq for Ordering

## Auto Trait Implementations§

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### impl Freeze for Ordering

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### impl RefUnwindSafe for Ordering

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### impl Send for Ordering

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### impl Sync for Ordering

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### impl Unpin for Ordering

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### impl UnwindSafe for Ordering

## Blanket Implementations§

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### impl<T> Any for T
where T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for T
where T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for T
where T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> CloneToUninit for T
where T: Clone,

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#### unsafe fn clone_to_uninit(&self, dest: *mut u8)

🔬This is a nightly-only experimental API. (`clone_to_uninit` #126799)
Performs copy-assignment from `self` to `dest`. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for T
where U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T> ToOwned for T
where T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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### impl<T, U> TryFrom<U> for T
where U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.