pub trait Ord: Eq + PartialOrd<Self> {
    fn cmp(&self, other: &Self) -> Ordering;

    fn max(self, other: Self) -> Self { ... }
fn min(self, other: Self) -> Self { ... }
fn clamp(self, min: Self, max: Self) -> Self { ... } }
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.

Corollaries

From the above and the requirements of PartialOrd, it follows that < defines a strict total order. This means 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 >.

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 sequence 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

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);

Provided methods

Compares and returns the maximum of two values.

Returns the second argument if the comparison determines them to be equal.

Examples
assert_eq!(2, 1.max(2));
assert_eq!(2, 2.max(2));

Compares and returns the minimum of two values.

Returns the first argument if the comparison determines them to be equal.

Examples
assert_eq!(1, 1.min(2));
assert_eq!(2, 2.min(2));

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!((-3).clamp(-2, 1) == -2);
assert!(0.clamp(-2, 1) == 0);
assert!(2.clamp(-2, 1) == 1);

Implementations on Foreign Types

Implements comparison of vectors lexicographically.

Implements comparison of arrays lexicographically.

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.

Comparison for two Rcs.

The two are compared by calling cmp() on their inner values.

Examples
use std::rc::Rc;
use std::cmp::Ordering;

let five = Rc::new(5);

assert_eq!(Ordering::Less, five.cmp(&Rc::new(6)));

Implements ordering of vectors, lexicographically.

Comparison for two Arcs.

The two are compared by calling cmp() on their inner values.

Examples
use std::sync::Arc;
use std::cmp::Ordering;

let five = Arc::new(5);

assert_eq!(Ordering::Less, five.cmp(&Arc::new(6)));

Implementors

impl<T, const CAP: usize> Ord for ArrayVec<T, CAP> where
    T: Ord

impl<const CAP: usize> Ord for ArrayString<CAP>

impl<T: Ord> Ord for CapacityError<T>

impl<'a> Ord for Components<'a>

impl Ord for Path

impl Ord for PathBuf

impl Ord for BigEndian

impl Ord for LittleEndian

impl Ord for Instant

impl Ord for SystemTime

impl Ord for NaiveDate

impl Ord for IsoWeek

impl Ord for NaiveTime

impl<Tz: TimeZone> Ord for Date<Tz>

impl<Tz: TimeZone> Ord for DateTime<Tz>

impl Ord for ConstantData

impl Ord for Block

impl Ord for Value

impl Ord for Inst

impl Ord for StackSlot

impl Ord for DynamicType

impl Ord for GlobalValue

impl Ord for Constant

impl Ord for Immediate

impl Ord for JumpTable

impl Ord for FuncRef

impl Ord for SigRef

impl Ord for Heap

impl Ord for Table

impl Ord for AnyEntity

impl<T: Ord + ReservedValue> Ord for PackedOption<T>

impl<T: ?Sized + Pointable> Ord for Shared<'_, T>

impl<L: Ord, R: Ord> Ord for Either<L, R>

impl<T: Ord> Ord for AssertAsync<T>

impl<T: Ord> Ord for AllowStdIo<T>

impl<T: Ord, N> Ord for GenericArray<T, N> where
    N: ArrayLength<T>, 

impl Ord for Register

impl<T: Ord> Ord for DebugInfoOffset<T>

impl<T: Ord> Ord for DebugTypesOffset<T>

impl<T: Ord> Ord for UnitSectionOffset<T>

impl Ord for SectionId

impl Ord for DwSect

impl Ord for DwSectV2

impl Ord for DwUt

impl Ord for DwCfa

impl Ord for DwChildren

impl Ord for DwTag

impl Ord for DwAt

impl Ord for DwForm

impl Ord for DwAte

impl Ord for DwLle

impl Ord for DwDs

impl Ord for DwEnd

impl Ord for DwAccess

impl Ord for DwVis

impl Ord for DwVirtuality

impl Ord for DwLang

impl Ord for DwAddr

impl Ord for DwId

impl Ord for DwCc

impl Ord for DwInl

impl Ord for DwOrd

impl Ord for DwDsc

impl Ord for DwIdx

impl Ord for DwDefaulted

impl Ord for DwLns

impl Ord for DwLne

impl Ord for DwLnct

impl Ord for DwMacro

impl Ord for DwRle

impl Ord for DwOp

impl Ord for DwEhPe

impl Ord for ArangeEntry

impl Ord for ColumnType

impl<T: Ord> Ord for UnitOffset<T>

impl Ord for IpAddrRange

impl Ord for IpNet

impl Ord for Ipv4Net

impl Ord for Ipv6Net

impl Ord for IpSubnets

impl Ord for Ipv4Subnets

impl Ord for Ipv6Subnets

impl<K: Hash + Eq + Ord, V: Ord, S: BuildHasher> Ord for LinkedHashMap<K, V, S>

impl<Storage: Ord> Ord for __BindgenBitfieldUnit<Storage>

impl<'k> Ord for Key<'k>

impl Ord for Level

impl Ord for LevelFilter

impl<'a> Ord for Metadata<'a>

impl<'a> Ord for MetadataBuilder<'a>

impl<T: Ord> Ord for MaybeOwned<'_, T>

impl<T: Ord> Ord for MaybeOwnedMut<'_, T>

impl<E: Ord + Endian> Ord for U16<E>

impl<E: Ord + Endian> Ord for U32<E>

impl<E: Ord + Endian> Ord for U64<E>

impl<E: Ord + Endian> Ord for I16<E>

impl<E: Ord + Endian> Ord for I32<E>

impl<E: Ord + Endian> Ord for I64<E>

impl<E: Ord + Endian> Ord for U16Bytes<E>

impl<E: Ord + Endian> Ord for U32Bytes<E>

impl<E: Ord + Endian> Ord for U64Bytes<E>

impl<E: Ord + Endian> Ord for I16Bytes<E>

impl<E: Ord + Endian> Ord for I32Bytes<E>

impl<E: Ord + Endian> Ord for I64Bytes<E>

impl Ord for SectionIndex

impl Ord for SymbolIndex

impl Ord for SectionId

impl Ord for SymbolId

impl Ord for ComdatId

impl Ord for Ident

impl Ord for Inst

impl Ord for Block

impl Ord for RegClass

impl Ord for PReg

impl Ord for PRegSet

impl Ord for VReg

impl Ord for SpillSlot

impl Ord for Operand

impl Ord for Allocation

impl Ord for InstPosition

impl Ord for ProgPoint

impl Ord for Span

impl Ord for Position

impl Ord for Literal

impl Ord for Utf8Sequence

impl Ord for Utf8Range

impl Ord for FdFlags

impl Ord for Access

impl Ord for AtFlags

impl Ord for Mode

impl Ord for OFlags

impl Ord for ResolveFlags

impl Ord for RenameFlags

impl Ord for MemfdFlags

impl Ord for SealFlags

impl Ord for StatxFlags

impl Ord for CreateFlags

impl Ord for EventFlags

impl Ord for PollFlags

impl Ord for DupFlags

impl Ord for PipeFlags

impl Ord for EventfdFlags

impl Ord for ProtFlags

impl Ord for MapFlags

impl Ord for MremapFlags

impl Ord for MlockFlags

impl Ord for MsyncFlags

impl Ord for SendFlags

impl Ord for RecvFlags

impl Ord for AcceptFlags

impl Ord for SocketFlags

impl Ord for TimerfdFlags

impl Ord for WaitOptions

impl Ord for Certificate

impl Ord for SigId

impl<A: Array> Ord for SmallVec<A> where
    A::Item: Ord

impl Ord for Lifetime

impl Ord for FdFlags

impl Ord for Duration

impl Ord for Timespec

impl Ord for SteadyTime

impl Ord for Tm

impl<A: Array> Ord for ArrayVec<A> where
    A::Item: Ord

impl<'s, T> Ord for SliceVec<'s, T> where
    T: Ord

impl<A: Array> Ord for TinyVec<A> where
    A::Item: Ord

impl<T: Ord> Ord for Spanned<T>

impl Ord for Level

impl Ord for LevelFilter

impl Ord for FmtSpan

impl Ord for DNSClass

impl Ord for Label

impl Ord for Name

impl Ord for SvcParamKey

impl Ord for RData

impl Ord for RecordType

impl Ord for Record

impl Ord for B0

impl Ord for B1

impl<U: Ord + Unsigned + NonZero> Ord for PInt<U>

impl<U: Ord + Unsigned + NonZero> Ord for NInt<U>

impl Ord for Z0

impl Ord for UTerm

impl<U: Ord, B: Ord> Ord for UInt<U, B>

impl Ord for ATerm

impl<V: Ord, A: Ord> Ord for TArr<V, A>

impl Ord for Greater

impl Ord for Less

impl Ord for Equal

impl Ord for Level

impl<S: Ord> Ord for Host<S>

impl Ord for Url

impl Ord for Hyphenated

impl Ord for Simple

impl Ord for Urn

impl Ord for Braced

impl Ord for Uuid

impl<V: Ord> Ord for VecMap<V>

impl Ord for DirCaps

impl Ord for FdFlags

impl Ord for SdFlags

impl Ord for SiFlags

impl Ord for RiFlags

impl Ord for RoFlags

impl Ord for OFlags

impl Ord for FileCaps

impl Ord for RwEventFlags

impl Ord for Rights

impl Ord for Fdflags

impl Ord for Fstflags

impl Ord for Lookupflags

impl Ord for Oflags

impl Ord for Eventrwflags

impl Ord for Riflags

impl Ord for Roflags

impl Ord for Sdflags

impl Ord for Rights

impl Ord for Fdflags

impl Ord for Fstflags

impl Ord for Lookupflags

impl Ord for Oflags

impl Ord for Eventrwflags

impl Ord for Riflags

impl Ord for Roflags

impl Ord for Sdflags

impl Ord for ValType

impl Ord for SectionId

impl<'a> Ord for SectionCode<'a>

impl Ord for FuncIndex

impl Ord for TableIndex

impl Ord for GlobalIndex

impl Ord for MemoryIndex

impl Ord for DataIndex

impl Ord for ElemIndex

impl Ord for TypeIndex

impl Ord for TagIndex

impl Ord for EntityIndex

impl Ord for Span

impl Ord for SizeAlign