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 { ... }
}
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.
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 == b
ora > b
is true; and <
is transitive:a < b
andb < c
impliesa < 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 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 primarily by their discriminants.
Secondarily, they are ordered by their fields.
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);
RunHowever, 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 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
}
}
RunRequired Methods§
sourcefn cmp(&self, other: &Self) -> Ordering
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);
RunProvided Methods§
1.50.0 · sourcefn clamp(self, min: Self, max: Self) -> Selfwhere
Self: Sized + PartialOrd,
fn clamp(self, min: Self, max: Self) -> Selfwhere
Self: Sized + PartialOrd,
Object Safety§
Implementors§
impl Ord for AsciiChar
impl Ord for Infallible
impl Ord for ErrorKind
impl Ord for IpAddr
impl Ord for SocketAddr
impl Ord for Ordering
impl Ord for bool
impl Ord for char
impl Ord for i8
impl Ord for i16
impl Ord for i32
impl Ord for i64
impl Ord for i128
impl Ord for isize
impl Ord for !
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.
impl Ord for u8
impl Ord for u16
impl Ord for u32
impl Ord for u64
impl Ord for u128
impl Ord for ()
impl Ord for usize
impl Ord for CpuidResult
impl Ord for TypeId
impl Ord for CStr
impl Ord for CString
impl Ord for OsStr
impl Ord for OsString
impl Ord for Error
impl Ord for PhantomPinned
impl Ord for Ipv4Addr
impl Ord for Ipv6Addr
impl Ord for SocketAddrV4
impl Ord for SocketAddrV6
impl Ord for NonZero<i8>
impl Ord for NonZero<i16>
impl Ord for NonZero<i32>
impl Ord for NonZero<i64>
impl Ord for NonZero<i128>
impl Ord for NonZero<isize>
impl Ord for NonZero<u8>
impl Ord for NonZero<u16>
impl Ord for NonZero<u32>
impl Ord for NonZero<u64>
impl Ord for NonZero<u128>
impl Ord for NonZero<usize>
impl Ord for Components<'_>
impl Ord for Path
impl Ord for PathBuf
impl Ord for PrefixComponent<'_>
impl Ord for Alignment
impl Ord for String
impl Ord for Duration
impl Ord for Instant
impl Ord for SystemTime
impl<'a> Ord for Component<'a>
impl<'a> Ord for Prefix<'a>
impl<'a> Ord for Location<'a>
impl<A> Ord for &A
impl<A> Ord for &mut A
impl<B> Ord for Cow<'_, B>
impl<Dyn> Ord for DynMetadata<Dyn>where
Dyn: ?Sized,
impl<F> Ord for Fwhere
F: FnPtr,
impl<K, V, A> Ord for BTreeMap<K, V, A>
impl<Ptr> Ord for Pin<Ptr>
impl<T> Ord for Option<T>where
T: Ord,
impl<T> Ord for Poll<T>where
T: Ord,
impl<T> Ord for *const Twhere
T: ?Sized,
impl<T> Ord for *mut Twhere
T: ?Sized,
impl<T> Ord for [T]where
T: Ord,
Implements comparison of vectors lexicographically.
impl<T> Ord for (T₁, T₂, …, Tₙ)
This trait is implemented for tuples up to twelve items long.
impl<T> Ord for Cell<T>
impl<T> Ord for RefCell<T>
impl<T> Ord for PhantomData<T>where
T: ?Sized,
impl<T> Ord for ManuallyDrop<T>
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>
impl<T, A> Ord for BTreeSet<T, A>
impl<T, A> Ord for LinkedList<T, A>
impl<T, A> Ord for VecDeque<T, A>
impl<T, A> Ord for Rc<T, A>
impl<T, A> Ord for Arc<T, A>
impl<T, A> Ord for Vec<T, A>
Implements ordering of vectors, lexicographically.
impl<T, E> Ord for Result<T, E>
impl<T, const N: usize> Ord for [T; N]where
T: Ord,
Implements comparison of arrays lexicographically.