Enum std::cmp::Ordering

pub enum Ordering {
    Less,
    Equal,
    Greater,
}

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

Examples

use std::cmp::Ordering;

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

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

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

Variants

Less

An ordering where a compared value is less [than another].

Equal

An ordering where a compared value is equal [to another].

Greater

An ordering where a compared value is greater [than another].

Methods

impl Ordering

fn reverse(self) -> Ordering

Reverse 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 mut 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);

fn then(self, other: Ordering) -> Ordering

🔬 This is a nightly-only experimental API.   (ordering_chaining)

Chains two orderings.

Returns self when it's not Equal. Otherwise returns other.

Examples

#![feature(ordering_chaining)]

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);

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

🔬 This is a nightly-only experimental API.   (ordering_chaining)

Chains the ordering with the given function.

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

Examples

#![feature(ordering_chaining)]

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

impl Ord for Ordering

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

This method returns an Ordering between self and other.

impl Hash for Ordering

fn hash<__H>(&self, __arg_0: &mut __H) where __H: Hasher

Feeds this value into the state given, updating the hasher as necessary.

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

Feeds a slice of this type into the state provided.

impl PartialOrd<Ordering> for Ordering

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

This method returns an ordering between self and other values if one exists.

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

This method tests less than (for self and other) and is used by the < operator.

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

This method tests less than or equal to (for self and other) and is used by the <= operator.

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

This method tests greater than (for self and other) and is used by the > operator.

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

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl PartialEq<Ordering> for Ordering

fn eq(&self, __arg_0: &Ordering) -> bool

This method tests for self and other values to be equal, and is used by ==.

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

This method tests for !=.

impl Clone for Ordering

fn clone(&self) -> Ordering

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Eq for Ordering

impl Copy for Ordering

impl Debug for Ordering

fn fmt(&self, __arg_0: &mut Formatter) -> Result<(), Error>

Formats the value using the given formatter.