Trait std::marker::StructuralEq

source ·

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 StructuralPartialEq 和 Eq 的幼稚检查。

要解决此问题，我们使用两个派生对象 (#[derive(PartialEq)] 和 #[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。

Trait std::marker::StructuralEq

Background

Implementors§

impl StructuralEq for AsciiChar

impl StructuralEq for BacktraceStatus

impl StructuralEq for std::cmp::Ordering

impl StructuralEq for TryReserveErrorKind

impl StructuralEq for VarError

impl StructuralEq for std::fmt::Alignment

impl StructuralEq for ErrorKind

impl StructuralEq for SeekFrom

impl StructuralEq for IpAddr

impl StructuralEq for Ipv6MulticastScope

impl StructuralEq for Shutdown

impl StructuralEq for SocketAddr

impl StructuralEq for FpCategory

impl StructuralEq for IntErrorKind

impl StructuralEq for BacktraceStyle

impl StructuralEq for Which

impl StructuralEq for SearchStep

impl StructuralEq for std::sync::atomic::Ordering

impl StructuralEq for RecvTimeoutError

impl StructuralEq for TryRecvError

impl StructuralEq for bool

impl StructuralEq for char

impl StructuralEq for i8

impl StructuralEq for i16

impl StructuralEq for i32

impl StructuralEq for i64

impl StructuralEq for i128

impl StructuralEq for isize

impl StructuralEq for str

impl StructuralEq for u8

impl StructuralEq for u16

impl StructuralEq for u32

impl StructuralEq for u64

impl StructuralEq for u128

impl StructuralEq for usize

impl StructuralEq for CpuidResult

impl StructuralEq for FromBytesUntilNulError

impl StructuralEq for AllocError

impl StructuralEq for Layout

impl StructuralEq for LayoutError

impl StructuralEq for TypeId

impl StructuralEq for CharTryFromError

impl StructuralEq for DecodeUtf16Error

impl StructuralEq for ParseCharError

impl StructuralEq for TryFromCharError

impl StructuralEq for TryReserveError

impl StructuralEq for CString

impl StructuralEq for FromBytesWithNulError

impl StructuralEq for FromVecWithNulError

impl StructuralEq for IntoStringError

impl StructuralEq for NulError

impl StructuralEq for Error

impl StructuralEq for FileType

impl StructuralEq for Permissions

impl StructuralEq for Assume

impl StructuralEq for AddrParseError

impl StructuralEq for Ipv4Addr

impl StructuralEq for Ipv6Addr

impl StructuralEq for SocketAddrV4

impl StructuralEq for SocketAddrV6

impl StructuralEq for NonZeroI8

impl StructuralEq for NonZeroI16

impl StructuralEq for NonZeroI32

impl StructuralEq for NonZeroI64

impl StructuralEq for NonZeroI128

impl StructuralEq for NonZeroIsize

impl StructuralEq for NonZeroU8

impl StructuralEq for NonZeroU16

impl StructuralEq for NonZeroU32

impl StructuralEq for NonZeroU64

impl StructuralEq for NonZeroU128

impl StructuralEq for NonZeroUsize

impl StructuralEq for ParseFloatError

impl StructuralEq for ParseIntError

impl StructuralEq for TryFromIntError

impl StructuralEq for RangeFull

impl StructuralEq for UCred