Trait std::marker::StructuralEq

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

Required trait for constants used in pattern matches.

Any type that derives Eq automatically implements this trait, regardless of whether its type parameters implement Eq.

This is a hack to work around a limitation in our type system.

§Background

We want to require that types of consts used in pattern matches have the attribute #[derive(PartialEq, Eq)].

In a more ideal world, we could check that requirement by just checking that the given type implements both the StructuralPartialEq trait and the Eq trait. However, you can have ADTs that do derive(PartialEq, Eq), and be a case that we want the compiler to accept, and yet the constant’s type fails to implement Eq.

Namely, a case like this:

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

fn higher_order(_: &()) { }

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

#[allow(pointer_structural_match)]
fn main() {
    match CFN {
        CFN => {}
        _ => {}
    }
}
Run

(The problem in the above code is that Wrap<fn(&())> does not implement PartialEq, nor Eq, because for<'a> fn(&'a _) does not implement those traits.)

Therefore, we cannot rely on naive check for StructuralPartialEq and mere Eq.

As a hack to work around this, we use two separate traits injected by each of the two derives (#[derive(PartialEq)] and #[derive(Eq)]) and check that both of them are present as part of structural-match checking.

Implementors§

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impl StructuralEq for AsciiChar

1.65.0 · source§

impl StructuralEq for BacktraceStatus

1.0.0 · source§

impl StructuralEq for std::cmp::Ordering

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impl StructuralEq for TryReserveErrorKind

1.0.0 · source§

impl StructuralEq for VarError

1.28.0 · source§

impl StructuralEq for std::fmt::Alignment

1.0.0 · source§

impl StructuralEq for ErrorKind

1.0.0 · source§

impl StructuralEq for SeekFrom

1.7.0 · source§

impl StructuralEq for IpAddr

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impl StructuralEq for Ipv6MulticastScope

1.0.0 · source§

impl StructuralEq for Shutdown

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 BacktraceStyle

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impl StructuralEq for Which

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impl StructuralEq for SearchStep

1.0.0 · source§

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

1.12.0 · source§

impl StructuralEq for RecvTimeoutError

1.0.0 · source§

impl StructuralEq for TryRecvError

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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 ()

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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

1.34.0 · 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

1.57.0 · source§

impl StructuralEq for TryReserveError

1.64.0 · source§

impl StructuralEq for CString

1.69.0 · source§

impl StructuralEq for FromBytesUntilNulError

1.64.0 · source§

impl StructuralEq for FromBytesWithNulError

1.64.0 · source§

impl StructuralEq for FromVecWithNulError

1.64.0 · source§

impl StructuralEq for IntoStringError

1.64.0 · source§

impl StructuralEq for NulError

1.0.0 · source§

impl StructuralEq for Error

1.1.0 · source§

impl StructuralEq for FileType

1.0.0 · source§

impl StructuralEq for Permissions

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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 UCred

Available on Unix only.
1.63.0 · source§

impl StructuralEq for InvalidHandleError

Available on Windows only.
1.63.0 · source§

impl StructuralEq for NullHandleError

Available on Windows only.
1.7.0 · source§

impl StructuralEq for StripPrefixError

1.0.0 · source§

impl StructuralEq for ExitStatus

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impl StructuralEq for ExitStatusError

1.0.0 · source§

impl StructuralEq for Output

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impl StructuralEq for std::ptr::Alignment

1.0.0 · source§

impl StructuralEq for ParseBoolError

1.0.0 · source§

impl StructuralEq for Utf8Error

1.0.0 · source§

impl StructuralEq for FromUtf8Error

1.0.0 · source§

impl StructuralEq for String

1.0.0 · source§

impl StructuralEq for RecvError

1.5.0 · source§

impl StructuralEq for WaitTimeoutResult

1.26.0 · source§

impl StructuralEq for AccessError

1.19.0 · source§

impl StructuralEq for ThreadId

1.3.0 · source§

impl StructuralEq for Duration

1.8.0 · source§

impl StructuralEq for Instant

1.8.0 · source§

impl StructuralEq for SystemTime

1.66.0 · source§

impl StructuralEq for TryFromFloatSecsError

1.27.0 · source§

impl StructuralEq for CpuidResult

1.33.0 · source§

impl StructuralEq for PhantomPinned

1.0.0 · source§

impl<'a> StructuralEq for Component<'a>

1.0.0 · source§

impl<'a> StructuralEq for Prefix<'a>

1.10.0 · source§

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

1.0.0 · source§

impl<'a> StructuralEq for PrefixComponent<'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>

1.0.0 · source§

impl<T> StructuralEq for TrySendError<T>

1.36.0 · source§

impl<T> StructuralEq for Poll<T>

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impl<T> StructuralEq for &Twhere T: ?Sized,

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impl<T> StructuralEq for [T]

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

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

1.19.0 · source§

impl<T> StructuralEq for Reverse<T>

1.0.0 · source§

impl<T> StructuralEq for Cursor<T>

1.20.0 · source§

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

1.74.0 · source§

impl<T> StructuralEq for Saturating<T>

1.0.0 · source§

impl<T> StructuralEq for Wrapping<T>

1.0.0 · source§

impl<T> StructuralEq for SendError<T>

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

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<Y, R> StructuralEq for CoroutineState<Y, R>