Trait scale_info::prelude::marker::StructuralEq

#[lang = "structural_teq"]pub trait StructuralEq { }

🔬 This is a nightly-only experimental API. (structural_match)

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);

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

(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.

Implementations on Foreign Types

impl StructuralEq for Shutdown

impl StructuralEq for Output

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

impl StructuralEq for UCred

impl<T> StructuralEq for SendError<T>

impl<T> StructuralEq for Cursor<T>

impl StructuralEq for VarError

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

impl StructuralEq for TryRecvError

impl StructuralEq for ExitStatus

impl StructuralEq for IntoStringError

impl StructuralEq for SystemTime

impl StructuralEq for Ipv6MulticastScope

impl StructuralEq for RecvTimeoutError

impl StructuralEq for StripPrefixError

impl StructuralEq for FileType

impl StructuralEq for Instant

impl StructuralEq for WaitTimeoutResult

impl StructuralEq for SocketAddr

impl StructuralEq for AccessError

impl StructuralEq for SeekFrom

impl StructuralEq for IpAddr

impl StructuralEq for ErrorKind

impl StructuralEq for Permissions

impl<'a> StructuralEq for PrefixComponent<'a>

impl StructuralEq for FromVecWithNulError

impl StructuralEq for AddrParseError

impl StructuralEq for RecvError

impl StructuralEq for NulError

impl StructuralEq for FromBytesWithNulError

impl StructuralEq for CString

impl StructuralEq for ThreadId

impl StructuralEq for BacktraceStatus

impl<T> StructuralEq for TrySendError<T>

impl<'a> StructuralEq for Utf8LossyChunk<'a>

impl<Idx> StructuralEq for RangeFrom<Idx>

impl StructuralEq for Duration

impl<Idx> StructuralEq for RangeTo<Idx>

impl StructuralEq for CpuidResult

impl<Idx> StructuralEq for RangeInclusive<Idx>

impl StructuralEq for ParseCharError

impl<T> StructuralEq for Option<T>

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

impl StructuralEq for DecodeUtf16Error

impl<Idx> StructuralEq for RangeToInclusive<Idx>

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

impl StructuralEq for LayoutError

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

impl StructuralEq for SearchStep

impl StructuralEq for ParseBoolError

impl StructuralEq for RangeFull

impl StructuralEq for Ordering

impl StructuralEq for AllocError

impl<T> StructuralEq for Poll<T>

impl StructuralEq for Layout

impl<Idx> StructuralEq for Range<Idx>

impl StructuralEq for NoneError

impl StructuralEq for CharTryFromError

impl StructuralEq for Utf8Error

impl StructuralEq for Error

impl StructuralEq for OptionBool

impl<T> StructuralEq for Compact<T>

impl<T> StructuralEq for CapacityError<T>

impl StructuralEq for Error

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Implementors

impl StructuralEq for PathError

impl StructuralEq for TypeDefPrimitive

impl StructuralEq for MetaForm

impl StructuralEq for TryReserveError

impl StructuralEq for FpCategory

impl StructuralEq for IntErrorKind

impl StructuralEq for TypeId

impl StructuralEq for scale_info::prelude::fmt::Error

impl StructuralEq for PhantomPinned

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 FromUtf8Error

impl StructuralEq for String

impl StructuralEq for Registry

impl<'a, T> StructuralEq for Symbol<'a, T>

impl<S> StructuralEq for PortableForm<S>

impl<S> StructuralEq for PortableRegistry<S> where
    S: FormString, 

impl<T> StructuralEq for Bound<T>

impl<T> StructuralEq for Interner<T>

impl<T> StructuralEq for UntrackedSymbol<T>

impl<T> StructuralEq for Reverse<T>

impl<T> StructuralEq for BTreeSet<T>

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

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

impl<T> StructuralEq for Wrapping<T>

impl<T: Form> StructuralEq for TypeDef<T>

impl<T: Form> StructuralEq for Field<T>

impl<T: Form> StructuralEq for Path<T>

impl<T: Form> StructuralEq for Type<T>

impl<T: Form> StructuralEq for TypeDefArray<T>

impl<T: Form> StructuralEq for TypeDefComposite<T>

impl<T: Form> StructuralEq for TypeDefPhantom<T>

impl<T: Form> StructuralEq for TypeDefSequence<T>

impl<T: Form> StructuralEq for TypeDefTuple<T>

impl<T: Form> StructuralEq for TypeDefVariant<T>

impl<T: Form> StructuralEq for Variant<T>

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