```
pub trait Ord: Eq + PartialOrd<Self> {
// 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`

or`a > b`

is true; and `<`

is transitive:`a < b`

and`b < c`

implies`a < 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
}
}
```

Run## Required Methods§

source#### fn 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);
```

Run## Provided Methods§

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

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

## Object Safety§

**not**object safe.

## Implementors§

### impl Ord for AsciiChar

### impl Ord for Infallible

### 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 TypeId

### impl Ord for CpuidResult

**x86 or x86-64**only.

### impl Ord for CStr

### 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 Alignment

### impl Ord for Duration

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

### impl<A> Ord for &A

### impl<A> Ord for &mut A

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

### impl<F: FnPtr> Ord for F

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

### impl<T> Ord for (T₁, T₂, …, Tₙ)

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

### impl<T> Ord for NonZero<T>where
T: ZeroablePrimitive + Ord,

### impl<T, const N: usize> Ord for Simd<T, N>

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

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

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

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

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

Implements comparison of vectors lexicographically.

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

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

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

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

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

Implements comparison of arrays lexicographically.