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Trait std::cmp::PartialOrd ​

一个用于形成 [部分顺序]partial order 的类型的 trait。

rust
pub trait PartialOrd<Rhs = Self>: PartialEq<Rhs>
where
    Rhs: ?Sized,
{
    // Required method
    fn partial_cmp(&self, other: &Rhs) -> Option<Ordering>;

    // Provided methods
    fn lt(&self, other: &Rhs) -> bool { ... }
    fn le(&self, other: &Rhs) -> bool { ... }
    fn gt(&self, other: &Rhs) -> bool { ... }
    fn ge(&self, other: &Rhs) -> bool { ... }
}

此 trait 的 lt、le、gt 和 ge 方法可以分别使用 <、<=、> 和 >= 相互调用。

这个 trait 的方法必须相互一致，并且与 PartialEq 的方法一致。 必须满足以下条件:

  1. a == b 当且仅当 partial_cmp(a, b) == Some(Equal)。
  2. a < b 当且仅当 partial_cmp(a, b) == Some(Less)
  3. a > b 当且仅当 partial_cmp(a, b) == Some(Greater)
  4. a <= b 当且仅当 a < b || a == b
  5. a >= b 当且仅当 a > b || a == b
  6. a != b 当且仅当 !(a == b)。

上述条件 2-5 默认实现保证。 PartialEq 已经保证了条件 6。

rust
let x: u32 = 0;
let y: u32 = 1;

assert_eq!(x < y, true);
assert_eq!(x.lt(&y), true);

如果Ord也为 Self 和 Rhs 实现，它也必须与 partial_cmp 一致 (具体要求请参见 trait 的文档)。 通过派生一些 traits 并手动实现其他一些行为，很容易使它们不以为然。

对于所有 a，b 和 c，比较必须满足：

  • 可传递性: a < b 和 b < c 表示 a < c。== 和 > 必须保持相同。
  • 二元性: a < b 当且仅当 b > a。

请注意，这些要求意味着 trait 本身必须对称且可传递地实现：如果 T: PartialOrd<U> 和 U: PartialOr\<V>，则 U: PartialOrd<T> 和 T: PartialOrd<V>。

Corollaries

从上述要求得出以下推论：

  • < 和 > 的非反射性: !(a < a)、!(a > a)
  • > 的传递性：如果 a > b 并且 b > c，则 a > c
  • partial_cmp 的对偶性: partial_cmp(a, b) == partial_cmp(b, a).map(Ordering::reverse)

Derivable ​

::: derive

该 trait 可以与 #[derive] 一起使用。

在结构体上 derive d 时，它将基于结构体成员的自上而下的声明顺序生成 词典 顺序。

当在枚举上 derived 时，变体按其判别式排序。 默认情况下，对于顶部的变体，判别式最小，底部变体的判别式最大。下面是一个例子：

rust
#[derive(PartialEq, PartialOrd)]
enum E {
    Top,
    Bottom,
}

assert!(E::Top < E::Bottom);

但是，手动设置判别式可以覆盖此默认行为:

rust
#[derive(PartialEq, PartialOrd)]
enum E {
    Top = 2,
    Bottom = 1,
}

assert!(E::Bottom < E::Top);

如何实现 PartialOrd？ ​

PartialOrd 只需要实现 partial_cmp 方法，其他方法从默认实现中生成。

但是，对于没有总顺序的类型，仍然可以单独实现其他类型。例如，对于浮点数，NaN < 0 == false 和 NaN >= 0 == false (参见 IEEE 754-2008 第 5.11 节)。

PartialOrd 要求您的类型为 PartialEq。

如果您的类型是 Ord，则可以使用 cmp 来实现 partial_cmp：

rust
use std::cmp::Ordering;

#[derive(Eq)]
struct Person {
    id: u32,
    name: String,
    height: u32,
}

impl PartialOrd for Person {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl Ord for Person {
    fn cmp(&self, other: &Self) -> Ordering {
        self.height.cmp(&other.height)
    }
}

impl PartialEq for Person {
    fn eq(&self, other: &Self) -> bool {
        self.height == other.height
    }
}

您可能还会发现在类型的字段上使用 partial_cmp 很有用。这是 Person 类型的示例，它们具有一个浮点 height 字段，该字段是唯一用于排序的字段：

rust
use std::cmp::Ordering;

struct Person {
    id: u32,
    name: String,
    height: f64,
}

impl PartialOrd for Person {
    fn partial_cmp(&self, other: &Self) -> Option\<Ordering> {
        self.height.partial_cmp(&other.height)
    }
}

impl PartialEq for Person {
    fn eq(&self, other: &Self) -> bool {
        self.height == other.height
    }
}

Required Methods ​

partial_cmp ​

如果存在，则此方法返回 self 和 other 值之间的顺序。

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

参数：

  • other：另一个需要比较的值

返回值：返回一个Option，若比较成功则返回Some(Ordering)，肉则返回None

rust
use std::cmp::Ordering;

let result = 1.0.partial_cmp(&2.0);
assert_eq!(result, Some(Ordering::Less));

let result = 1.0.partial_cmp(&1.0);
assert_eq!(result, Some(Ordering::Equal));

let result = 2.0.partial_cmp(&1.0);
assert_eq!(result, Some(Ordering::Greater));

如果无法进行比较：

rust
let result = f64::NAN.partial_cmp(&1.0);
assert_eq!(result, None);

Provided Methods ​

lt ​

比较另一个值是否小于self

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

参数：

  • other：另一个需要比较的值

返回值：根据比较的结果返回bool值

rust
assert_eq!(1.0 < 1.0, false);
assert_eq!(1.0 < 2.0, true);
assert_eq!(2.0 < 1.0, false);

le ​

比较另一个值是否小于等于self

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

参数：

  • other：另一个需要比较的值

返回值：根据比较的结果返回bool值

rust
assert_eq!(1.0 <= 1.0, true);
assert_eq!(1.0 <= 2.0, true);
assert_eq!(2.0 <= 1.0, false);

gt ​

比较另一个值是否大于self

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

参数：

  • other：另一个需要比较的值

返回值：根据比较的结果返回bool值

rust
assert_eq!(1.0 > 1.0, false);
assert_eq!(1.0 > 2.0, false);
assert_eq!(2.0 > 1.0, true);

ge ​

比较另一个值是否大于等于self

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

参数：

  • other：另一个需要比较的值

返回值：根据比较的结果返回bool值

rust
assert_eq!(1.0 >= 1.0, true);
assert_eq!(1.0 >= 2.0, false);
assert_eq!(2.0 >= 1.0, true);

​

Implementors ​

impl PartialOrd<AsciiChar> for AsciiChar ​

impl PartialOrd<Infallible> for Infallible ​

impl PartialOrd<ErrorKind> for ErrorKind ​

impl PartialOrd<IpAddr> for IpAddr ​

impl PartialOrd<IpAddr> for Ipv4Addr ​

impl PartialOrd<IpAddr> for Ipv6Addr ​

impl PartialOrd<SocketAddr> for SocketAddr ​

impl PartialOrd<Which> for Which ​

impl PartialOrd<Ordering> for Ordering ​

impl PartialOrd<bool> for bool ​

impl PartialOrd<char> for char ​

impl PartialOrd<f32> for f32 ​

impl PartialOrd<f64> for f64 ​

impl PartialOrd<i8> for i8 ​

impl PartialOrd<i16> for i16 ​

impl PartialOrd<i32> for i32 ​

impl PartialOrd<i64> for i64 ​

impl PartialOrd<i128> for i128 ​

impl PartialOrd<isize> for isize ​

impl PartialOrd<!> for ! ​

impl PartialOrd<str> for str ​

对字符串执行比较操作。

按字典顺序 通过字符串的字节值对字符串进行比较。 这将根据 Unicode 代码点在代码表中的位置进行比较。 这不一定与 “alphabetical” 顺序相同，后者因语言和区域设置而异。 根据文化认可的标准比较字符串需要特定于语言环境的数据，该数据不在 str 类型的作用域之内。

impl PartialOrd<str> for OsStr ​

impl PartialOrd<str> for OsString ​

impl PartialOrd<u8> for u8 ​

impl PartialOrd<u16> for u16 ​

impl PartialOrd<u32> for u32 ​

impl PartialOrd<u64> for u64 ​

impl PartialOrd<u128> for u128 ​

impl PartialOrd<()> for () ​

impl PartialOrd<usize> for usize ​

impl PartialOrd<CpuidResult> for CpuidResult ​

impl PartialOrd<TypeId> for TypeId ​

impl PartialOrd<CStr> for CStr ​

impl PartialOrd<CString> for CString ​

impl PartialOrd<OsStr> for OsStr ​

impl PartialOrd<OsStr> for Path ​

impl PartialOrd<OsStr> for PathBuf ​

impl PartialOrd<OsString> for OsString ​

impl PartialOrd<OsString> for Path ​

impl PartialOrd<OsString> for PathBuf ​

impl PartialOrd<Error> for Error ​

impl PartialOrd<PhantomPinned> for PhantomPinned ​

impl PartialOrd<Ipv4Addr> for IpAddr ​

impl PartialOrd<Ipv4Addr> for Ipv4Addr ​

impl PartialOrd<Ipv6Addr> for IpAddr ​

impl PartialOrd<Ipv6Addr> for Ipv6Addr ​

impl PartialOrd<SocketAddrV4> for SocketAddrV4 ​

impl PartialOrd<SocketAddrV6> for SocketAddrV6 ​

impl PartialOrd<NonZeroI8> for NonZeroI8 ​

impl PartialOrd<NonZeroI16> for NonZeroI16 ​

impl PartialOrd<NonZeroI32> for NonZeroI32 ​

impl PartialOrd<NonZeroI64> for NonZeroI64 ​

impl PartialOrd<NonZeroI128> for NonZeroI128 ​

impl PartialOrd<NonZeroIsize> for NonZeroIsize ​

impl PartialOrd<NonZeroU8> for NonZeroU8 ​

impl PartialOrd<NonZeroU16> for NonZeroU16 ​

impl PartialOrd<NonZeroU32> for NonZeroU32 ​

impl PartialOrd<NonZeroU64> for NonZeroU64 ​

impl PartialOrd<NonZeroU128> for NonZeroU128 ​

impl PartialOrd<NonZeroUsize> for NonZeroUsize ​

impl PartialOrd<Path> for OsStr ​

impl PartialOrd<Path> for OsString ​

impl PartialOrd<Path> for Path ​

impl PartialOrd<Path> for PathBuf ​

impl PartialOrd<PathBuf> for OsStr ​

impl PartialOrd<PathBuf> for OsString ​

impl PartialOrd<PathBuf> for Path ​

impl PartialOrd<PathBuf> for PathBuf ​

const: unstable ·

impl PartialOrd<Alignment> for Alignment ​

impl PartialOrd<String> for String ​

1.3.0 ·

impl PartialOrd<Duration> for Duration ​

impl PartialOrd<Instant> for Instant ​

impl PartialOrd<SystemTime> for SystemTime ​

impl<'a> PartialOrd<&'a OsStr> for Path ​

impl<'a> PartialOrd<&'a OsStr> for PathBuf ​

impl<'a> PartialOrd<&'a Path> for OsStr ​

impl<'a> PartialOrd<&'a Path> for OsString ​

impl<'a> PartialOrd<&'a Path> for PathBuf ​

impl<'a> PartialOrd<Cow<'a, OsStr>> for Path ​

impl<'a> PartialOrd<Cow<'a, OsStr>> for PathBuf ​

impl<'a> PartialOrd<Cow<'a, Path>> for OsStr ​

impl<'a> PartialOrd<Cow<'a, Path>> for OsString ​

impl<'a> PartialOrd<Cow<'a, Path>> for Path ​

impl<'a> PartialOrd<Cow<'a, Path>> for PathBuf ​

impl<'a> PartialOrd<Component<'a>> for Component<'a> ​

impl<'a> PartialOrd<Prefix<'a>> for Prefix<'a> ​

impl<'a> PartialOrd<OsStr> for &'a Path ​

impl<'a> PartialOrd<OsStr> for Cow<'a, Path> ​

impl<'a> PartialOrd<OsString> for &'a Path ​

impl<'a> PartialOrd<OsString> for Cow<'a, Path> ​

1.10.0 ·

impl<'a> PartialOrd<Location<'a>> for Location<'a> ​

impl<'a> PartialOrd<Components<'a>> for Components<'a> ​

impl<'a> PartialOrd<Path> for &'a OsStr ​

impl<'a> PartialOrd<Path> for Cow<'a, OsStr> ​

impl<'a> PartialOrd<Path> for Cow<'a, Path> ​

impl<'a> PartialOrd<PathBuf> for &'a OsStr ​

impl<'a> PartialOrd<PathBuf> for &'a Path ​

impl<'a> PartialOrd<PathBuf> for Cow<'a, OsStr> ​

impl<'a> PartialOrd<PathBuf> for Cow<'a, Path> ​

impl<'a> PartialOrd<PrefixComponent<'a>> for PrefixComponent<'a> ​

impl<'a, 'b> PartialOrd<&'a OsStr> for OsString ​

impl<'a, 'b> PartialOrd<&'a Path> for Cow<'b, OsStr> ​

impl<'a, 'b> PartialOrd<&'b OsStr> for Cow<'a, OsStr> ​

impl<'a, 'b> PartialOrd<&'b OsStr> for Cow<'a, Path> ​

impl<'a, 'b> PartialOrd<&'b Path> for Cow<'a, Path> ​

impl<'a, 'b> PartialOrd<Cow<'a, OsStr>> for &'b OsStr ​

impl<'a, 'b> PartialOrd<Cow<'a, OsStr>> for OsStr ​

impl<'a, 'b> PartialOrd<Cow<'a, OsStr>> for OsString ​

impl<'a, 'b> PartialOrd<Cow<'a, Path>> for &'b OsStr ​

impl<'a, 'b> PartialOrd<Cow<'a, Path>> for &'b Path ​

impl<'a, 'b> PartialOrd<Cow<'b, OsStr>> for &'a Path ​

impl<'a, 'b> PartialOrd<OsStr> for Cow<'a, OsStr> ​

impl<'a, 'b> PartialOrd<OsStr> for OsString ​

impl<'a, 'b> PartialOrd<OsString> for &'a OsStr ​

impl<'a, 'b> PartialOrd<OsString> for Cow<'a, OsStr> ​

impl<'a, 'b> PartialOrd<OsString> for OsStr ​

impl<'a, B> PartialOrd<Cow<'a, B>> for Cow<'a, B> ​

rust
impl<'a, B> PartialOrd<Cow<'a, B>> for Cow<'a, B>
where
  B: PartialOrd<B> + ToOwned + ?Sized,

impl<A, B> PartialOrd<&B> for &A ​

rust
impl<A, B> PartialOrd<&B> for &A
where
  A: PartialOrd<B> + ?Sized,
  B: ?Sized,

impl<A, B> PartialOrd<&mut B> for &mut A ​

rust
impl<A, B> PartialOrd<&mut B> for &mut A
where
  A: PartialOrd<B> + ?Sized,
  B: ?Sized,

impl<Dyn> PartialOrd<DynMetadata<Dyn>> for DynMetadata<Dyn> ​

rust
impl<Dyn> PartialOrd<DynMetadata<Dyn>> for DynMetadata<Dyn>
where
  Dyn: ?Sized,

impl<F> PartialOrd<F> for F ​

rust
impl<F> PartialOrd<F> for F
where
  F: FnPtr,

impl<K, V, A> PartialOrd<BTreeMap<K, V, A>> for BTreeMap<K, V, A> ​

rust
impl<K, V, A> PartialOrd<BTreeMap<K, V, A>> for BTreeMap<K, V, A>
where
  K: PartialOrd<K>,
  V: PartialOrd<V>,
  A: Allocator + Clone,

impl<P, Q> PartialOrd<Pin<Q>> for Pin<P> ​

rust
impl<P, Q> PartialOrd<Pin<Q>> for Pin<P>
where
  P: Deref,
  Q: Deref,
  <P as Deref>::Target: PartialOrd<<Q as Deref>::Target>,

impl<T> PartialOrd<Option<T>> for Option<T> ​

rust
impl<T> PartialOrd<Option<T>> for Option<T>
where
  T: PartialOrd<T>,

impl<T> PartialOrd<Poll<T>> for Poll<T> ​

rust
impl<T> PartialOrd<Poll<T>> for Poll<T>
where
  T: PartialOrd<T>,

impl<T> PartialOrd<*const T> for *const T ​

rust
impl<T> PartialOrd<*const T> for *const T
where
  T: ?Sized,

impl<T> PartialOrd<*mut T> for *mut T ​

rust
impl<T> PartialOrd<*mut T> for *mut T
where
  T: ?Sized,

impl<T> PartialOrd<[T]> for [T] ​

实现 vectors 按字典顺序 的比较。

rust
impl<T> PartialOrd<[T]> for [T]
where
  T: PartialOrd<T>,

impl<T> PartialOrd<(T,)> for (T₁, T₂, …, Tₙ) ​

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

rust
impl<T> PartialOrd<(T,)> for (T₁, T₂, …, Tₙ)
where
  T: PartialOrd<T> + ?Sized,

impl<T> PartialOrd<Cell<T>> for Cell<T> ​

rust
impl<T> PartialOrd<Cell<T>> for Cell<T>
where
  T: PartialOrd<T> + Copy,

impl<T> PartialOrd<RefCell<T>> for RefCell<T> ​

rust
impl<T> PartialOrd<RefCell<T>> for RefCell<T>
where
  T: PartialOrd<T> + ?Sized,

impl<T> PartialOrd<PhantomData<T>> for PhantomData<T> ​

rust
impl<T> PartialOrd<PhantomData<T>> for PhantomData<T>
where
  T: ?Sized,

impl<T> PartialOrd<ManuallyDrop<T>> for ManuallyDrop<T> ​

rust
impl<T> PartialOrd<ManuallyDrop<T>> for ManuallyDrop<T>
where
  T: PartialOrd<T> + ?Sized,

impl<T> PartialOrd<Saturating<T>> for Saturating<T> ​

rust
impl<T> PartialOrd<Saturating<T>> for Saturating<T>
where
  T: PartialOrd<T>,

impl<T> PartialOrd<Wrapping<T>> for Wrapping<T> ​

rust
impl<T> PartialOrd<Wrapping<T>> for Wrapping<T>
where
  T: PartialOrd<T>,

impl<T> PartialOrd<NonNull<T>> for NonNull<T> ​

rust
impl<T> PartialOrd<NonNull<T>> for NonNull<T>
where
  T: ?Sized,

impl<T> PartialOrd<Rc<T>> for Rc<T> ​

rust
impl<T> PartialOrd<Rc<T>> for Rc<T>
where
  T: PartialOrd<T> + ?Sized,

impl<T> PartialOrd<Arc<T>> for Arc<T> ​

rust
impl<T> PartialOrd<Arc<T>> for Arc<T>
where
  T: PartialOrd<T> + ?Sized,

impl<T> PartialOrd<Reverse<T>> for Reverse<T> ​

rust
impl<T> PartialOrd<Reverse<T>> for Reverse<T>
where
  T: PartialOrd<T>,

impl<T, A> PartialOrd<Box<T, A>> for Box<T, A> ​

rust
impl<T, A> PartialOrd<Box<T, A>> for Box<T, A>
where
  T: PartialOrd<T> + ?Sized,
  A: Allocator,

impl<T, A> PartialOrd<BTreeSet<T, A>> for BTreeSet<T, A> ​

rust
impl<T, A> PartialOrd<BTreeSet<T, A>> for BTreeSet<T, A>
where
  T: PartialOrd<T>,
  A: Allocator + Clone,

impl<T, A> PartialOrd<LinkedList<T, A>> for LinkedList<T, A> ​

rust
impl<T, A> PartialOrd<LinkedList<T, A>> for LinkedList<T, A>
where
  T: PartialOrd<T>,
  A: Allocator,

impl<T, A> PartialOrd<VecDeque<T, A>> for VecDeque<T, A> ​

rust
impl<T, A> PartialOrd<VecDeque<T, A>> for VecDeque<T, A>
where
  T: PartialOrd<T>,
  A: Allocator,

impl<T, A> PartialOrd<Vec<T, A>> for Vec<T, A> ​

实现 vectors、lexicographically 的比较。

rust
impl<T, A> PartialOrd<Vec<T, A>> for Vec<T, A>
where
  T: PartialOrd<T>,
  A: Allocator,

impl<T, E> PartialOrd<Result<T, E>> for Result<T, E> ​

rust
impl<T, E> PartialOrd<Result<T, E>> for Result<T, E>
where
  T: PartialOrd<T>,
  E: PartialOrd<E>,

impl<T, const LANES: usize> PartialOrd<Mask<T, LANES>> for Mask<T, LANES> ​

rust
impl<T, const LANES: usize> PartialOrd<Mask<T, LANES>> for Mask<T, LANES>
where
  T: MaskElement + PartialOrd<T>,
  LaneCount<LANES>: SupportedLaneCount,

impl<T, const N: usize> PartialOrd<[T; N]> for [T; N] ​

rust
impl<T, const N: usize> PartialOrd<[T; N]> for [T; N]
where
  T: PartialOrd<T>,

impl<T, const N: usize> PartialOrd<Simd<T, N>> for Simd<T, N> ​

rust
impl<T, const N: usize> PartialOrd<Simd<T, N>> for Simd<T, N>
where
  LaneCount<N>: SupportedLaneCount,
  T: SimdElement + PartialOrd<T>,

impl<Y, R> PartialOrd<GeneratorState<Y, R>> for GeneratorState<Y, R> ​

rust
impl<Y, R> PartialOrd<GeneratorState<Y, R>> for GeneratorState<Y, R>
where
  Y: PartialOrd<Y>,
  R: PartialOrd<R>,

impl PartialOrd<LineColumn> for LineColumn ​

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