Trait std::cmp::Ord
pub trait Ord: Eq + PartialOrd {
// Required method
fn cmp(&self, other: &Self) -> Ordering;
// Provided methods
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 + PartialOrd { ... }
}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.
Violating these requirements is a logic error. The behavior resulting from a logic error is not specified, but users of the trait must ensure that such logic errors do not result in undefined behavior. This means that unsafe code must not rely on the correctness of these methods.
Corollaries
From the above and the requirements of PartialOrd, it follows that for all a, b and c:
- exactly one of
a < b,a == bora > bis true; and <is transitive:a < bandb < cimpliesa < c. The same must hold for both==and>.
Mathematically speaking, the < operator defines a strict weak order. In cases where == conforms to mathematical equality, it also defines a strict total order.
Derivable
This trait can be used with #[derive].
When derived on structs, it will produce a lexicographic ordering based on the top-to-bottom declaration order of the struct’s members.
When derived 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);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);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 sequences 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
}
}Required Methods
fn cmp(&self, other: &Self) -> OrderingThis 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);Provided Methods
fn max(self, other: Self) -> Self
where
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!(1.max(2), 2);
assert_eq!(2.max(2), 2);fn min(self, other: Self) -> Self
where
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.min(2), 1);
assert_eq!(2.min(2), 2);fn clamp(self, min: Self, max: Self) -> Self
where
Self: Sized + 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_eq!((-3).clamp(-2, 1), -2);
assert_eq!(0.clamp(-2, 1), 0);
assert_eq!(2.clamp(-2, 1), 1);Object Safety
This trait is not object safe.
Implementors
impl Ord for AsciiCharimpl Ord for Infallibleimpl Ord for ErrorKindimpl Ord for IpAddrimpl Ord for SocketAddrimpl Ord for Whichimpl Ord for Orderingimpl Ord for boolimpl Ord for charimpl Ord for i8impl Ord for i16impl Ord for i32impl Ord for i64impl Ord for i128impl Ord for isizeimpl Ord for !impl Ord for strImplements 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.
impl Ord for u8impl Ord for u16impl Ord for u32impl Ord for u64impl Ord for u128impl Ord for ()impl Ord for usizeimpl Ord for CpuidResultimpl Ord for TypeIdimpl Ord for CStrimpl Ord for CStringimpl Ord for OsStrimpl Ord for OsStringimpl Ord for Errorimpl Ord for PhantomPinnedimpl Ord for Ipv4Addrimpl Ord for Ipv6Addrimpl Ord for SocketAddrV4impl Ord for SocketAddrV6impl Ord for NonZeroI8impl Ord for NonZeroI16impl Ord for NonZeroI32impl Ord for NonZeroI64impl Ord for NonZeroI128impl Ord for NonZeroIsizeimpl Ord for NonZeroU8impl Ord for NonZeroU16impl Ord for NonZeroU32impl Ord for NonZeroU64impl Ord for NonZeroU128impl Ord for NonZeroUsizeimpl Ord for Components<'_>impl Ord for Pathimpl Ord for PathBufimpl Ord for PrefixComponent<'_>impl Ord for Alignmentimpl Ord for Stringimpl Ord for Durationimpl Ord for Instantimpl Ord for SystemTimeimpl<'a> Ord for Component<'a>impl<'a> Ord for Prefix<'a>impl<'a> Ord for Location<'a>impl<A> Ord for &A
where
A: Ord + ?Sized,impl<A> Ord for &mut A
where
A: Ord + ?Sized,impl<B> Ord for Cow<'_, B>
where
B: Ord + ToOwned + ?Sized,impl<Dyn> Ord for DynMetadata<Dyn>
where
Dyn: ?Sized,impl<F> Ord for F
where
F: FnPtr,impl<K, V, A> Ord for BTreeMap<K, V, A>
where
K: Ord,
V: Ord,
A: Allocator + Clone,impl<P> Ord for Pin<P>
where
P: Deref,
<P as Deref>::Target: Ord,impl<T> Ord for Option<T>
where
T: Ord,impl<T> Ord for Poll<T>
where
T: Ord,impl<T> Ord for *const T
where
T: ?Sized,impl<T> Ord for *mut T
where
T: ?Sized,impl<T> Ord for [T]
where
T: Ord,Implements comparison of vectors lexicographically.
impl<T> Ord for (T₁, T₂, …, Tₙ)
where
T: Ord + ?Sized,This trait is implemented for tuples up to twelve items long.
impl<T> Ord for Cell<T>
where
T: Ord + Copy,impl<T> Ord for RefCell<T>
where
T: Ord + ?Sized,impl<T> Ord for PhantomData<T>
where
T: ?Sized,impl<T> Ord for ManuallyDrop<T>
where
T: Ord + ?Sized,impl<T> Ord for Saturating<T>
where
T: Ord,impl<T> Ord for Wrapping<T>
where
T: Ord,impl<T> Ord for NonNull<T>
where
T: ?Sized,impl<T> Ord for Reverse<T>
where
T: Ord,impl<T, A> Ord for Box<T, A>
where
T: Ord + ?Sized,
A: Allocator,impl<T, A> Ord for BTreeSet<T, A>
where
T: Ord,
A: Allocator + Clone,impl<T, A> Ord for LinkedList<T, A>
where
T: Ord,
A: Allocator,impl<T, A> Ord for VecDeque<T, A>
where
T: Ord,
A: Allocator,impl<T, A> Ord for Rc<T, A>
where
T: Ord + ?Sized,
A: Allocator,impl<T, A> Ord for Arc<T, A>
where
T: Ord + ?Sized,
A: Allocator,impl<T, A> Ord for Vec<T, A>
where
T: Ord,
A: Allocator,Implements ordering of vectors, lexicographically.
impl<T, E> Ord for Result<T, E>
where
T: Ord,
E: Ord,impl<T, const N: usize> Ord for [T; N]
where
T: Ord,Implements comparison of arrays lexicographically.
impl<T, const N: usize> Ord for Simd<T, N>
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement + Ord,impl<Y, R> Ord for CoroutineState<Y, R>
where
Y: Ord,
R: Ord,© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/cmp/trait.Ord.html