Trait core::marker::StructuralEq

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pub trait StructuralEq { }
🔬This is a nightly-only experimental API. (structural_match #31434)
Expand description

模式匹配中使用的常量的必需 trait。

派生 Eq 的任何类型都会自动实现此 trait,无论其类型参数是否实现 Eq

这是一种解决我们类型系统中的限制的技巧。

Background

我们要要求模式匹配中使用的 const 类型具有属性 #[derive(PartialEq, Eq)]

在更理想的世界中,我们可以通过仅检查给定类型是否同时实现 StructuralPartialEq trait 和 Eq trait 来检查该要求。 但是,您可能拥有 doderive(PartialEq, Eq) 的 ADT,这是我们希望编译器接受的情况,但是 const 的类型无法实现 Eq

也就是说,像这样的情况:

#[derive(PartialEq, Eq)]
struct Wrap<X>(X);

fn higher_order(_: &()) { }

const CFN: Wrap<fn(&())> = Wrap(higher_order);

fn main() {
    match CFN {
        CFN => {}
        _ => {}
    }
}
Run

(以上代码中的问题是 Wrap<fn(&())> 既不实现 PartialEq 也不实现 Eq,因为 for <'a> fn(&'a _) does not implement those traits.)

因此,我们不能仅仅依靠 StructuralPartialEqEq 的幼稚检查。

要解决此问题,我们使用两个派生对象 (#[derive(PartialEq)]#[derive(Eq)]) 中的每个派生注入的两个单独的 traits,并检查它们是否都作为结构匹配检查的一部分出现。

Implementors§

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impl StructuralEq for AsciiChar

1.0.0 · source§

impl StructuralEq for core::cmp::Ordering

1.28.0 · source§

impl StructuralEq for core::fmt::Alignment

1.7.0 · source§

impl StructuralEq for IpAddr

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impl StructuralEq for Ipv6MulticastScope

1.0.0 · source§

impl StructuralEq for SocketAddr

1.0.0 · source§

impl StructuralEq for FpCategory

1.55.0 · source§

impl StructuralEq for IntErrorKind

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impl StructuralEq for Which

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impl StructuralEq for SearchStep

1.0.0 · source§

impl StructuralEq for core::sync::atomic::Ordering

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impl StructuralEq for bool

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impl StructuralEq for char

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impl StructuralEq for i8

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impl StructuralEq for i16

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impl StructuralEq for i32

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impl StructuralEq for i64

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impl StructuralEq for i128

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impl StructuralEq for isize

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impl StructuralEq for str

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impl StructuralEq for u8

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impl StructuralEq for u16

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impl StructuralEq for u32

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impl StructuralEq for u64

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impl StructuralEq for u128

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impl StructuralEq for usize

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impl StructuralEq for AllocError

1.28.0 · source§

impl StructuralEq for Layout

1.50.0 · source§

impl StructuralEq for LayoutError

1.0.0 · source§

impl StructuralEq for TypeId

1.27.0 · source§

impl StructuralEq for CpuidResult

Available on x86 or x86-64 only.
1.34.0 · source§

impl StructuralEq for CharTryFromError

1.9.0 · source§

impl StructuralEq for DecodeUtf16Error

1.20.0 · source§

impl StructuralEq for ParseCharError

1.59.0 · source§

impl StructuralEq for TryFromCharError

1.69.0 · source§

impl StructuralEq for FromBytesUntilNulError

1.64.0 · source§

impl StructuralEq for FromBytesWithNulError

1.0.0 · source§

impl StructuralEq for Error

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impl StructuralEq for Assume

1.0.0 · source§

impl StructuralEq for AddrParseError

1.0.0 · source§

impl StructuralEq for Ipv4Addr

1.0.0 · source§

impl StructuralEq for Ipv6Addr

1.0.0 · source§

impl StructuralEq for SocketAddrV4

1.0.0 · source§

impl StructuralEq for SocketAddrV6

1.34.0 · source§

impl StructuralEq for NonZeroI8

1.34.0 · source§

impl StructuralEq for NonZeroI16

1.34.0 · source§

impl StructuralEq for NonZeroI32

1.34.0 · source§

impl StructuralEq for NonZeroI64

1.34.0 · source§

impl StructuralEq for NonZeroI128

1.34.0 · source§

impl StructuralEq for NonZeroIsize

1.28.0 · source§

impl StructuralEq for NonZeroU8

1.28.0 · source§

impl StructuralEq for NonZeroU16

1.28.0 · source§

impl StructuralEq for NonZeroU32

1.28.0 · source§

impl StructuralEq for NonZeroU64

1.28.0 · source§

impl StructuralEq for NonZeroU128

1.28.0 · source§

impl StructuralEq for NonZeroUsize

1.0.0 · source§

impl StructuralEq for ParseFloatError

1.0.0 · source§

impl StructuralEq for ParseIntError

1.34.0 · source§

impl StructuralEq for TryFromIntError

1.0.0 · source§

impl StructuralEq for RangeFull

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impl StructuralEq for core::ptr::Alignment

1.0.0 · source§

impl StructuralEq for ParseBoolError

1.0.0 · source§

impl StructuralEq for Utf8Error

1.3.0 · source§

impl StructuralEq for Duration

1.66.0 · source§

impl StructuralEq for TryFromFloatSecsError

1.33.0 · source§

impl StructuralEq for PhantomPinned

1.10.0 · source§

impl<'a> StructuralEq for Location<'a>

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impl<'a> StructuralEq for Utf8Chunk<'a>

1.55.0 · source§

impl<B, C> StructuralEq for ControlFlow<B, C>

1.0.0 · source§

impl<Idx> StructuralEq for Range<Idx>

1.0.0 · source§

impl<Idx> StructuralEq for RangeFrom<Idx>

1.26.0 · source§

impl<Idx> StructuralEq for RangeInclusive<Idx>

1.0.0 · source§

impl<Idx> StructuralEq for RangeTo<Idx>

1.26.0 · source§

impl<Idx> StructuralEq for RangeToInclusive<Idx>

1.17.0 · source§

impl<T> StructuralEq for Bound<T>

1.0.0 · source§

impl<T> StructuralEq for Option<T>

1.36.0 · source§

impl<T> StructuralEq for Poll<T>

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impl<T> StructuralEq for [T]

1.19.0 · source§

impl<T> StructuralEq for Reverse<T>

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impl<T> StructuralEq for Saturating<T>

1.0.0 · source§

impl<T> StructuralEq for Wrapping<T>

1.0.0 · source§

impl<T, E> StructuralEq for Result<T, E>

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

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impl<T: ?Sized> StructuralEq for &T

1.20.0 · source§

impl<T: ?Sized> StructuralEq for ManuallyDrop<T>

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impl<T: ?Sized> StructuralEq for PhantomData<T>

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impl<Y, R> StructuralEq for GeneratorState<Y, R>