[][src]Trait std::marker::StructuralEq

#[lang = "structural_teq"]pub trait StructuralEq { }
🔬 This is a nightly-only experimental API. (structural_match #31434)

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 workaround 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 (1.) the StructuralPartialEq trait and (2.) 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 => {}
        _ => {}
    }
}
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

impl StructuralEq for BacktraceStatus[src]

impl StructuralEq for VarError[src]

impl StructuralEq for ErrorKind[src]

impl StructuralEq for SeekFrom[src]

impl StructuralEq for IpAddr[src]

impl StructuralEq for Ipv6MulticastScope[src]

impl StructuralEq for Shutdown[src]

impl StructuralEq for SocketAddr[src]

impl StructuralEq for RecvTimeoutError[src]

impl StructuralEq for TryRecvError[src]

impl StructuralEq for CString[src]

impl StructuralEq for FromBytesWithNulError[src]

impl StructuralEq for FromVecWithNulError[src]

impl StructuralEq for IntoStringError[src]

impl StructuralEq for NulError[src]

impl StructuralEq for FileType[src]

impl StructuralEq for Permissions[src]

impl StructuralEq for AddrParseError[src]

impl StructuralEq for StripPrefixError[src]

impl StructuralEq for ExitStatus[src]

impl StructuralEq for Output[src]

impl StructuralEq for RecvError[src]

impl StructuralEq for WaitTimeoutResult[src]

impl StructuralEq for AccessError[src]

impl StructuralEq for ThreadId[src]

impl StructuralEq for Instant[src]

impl StructuralEq for SystemTime[src]

impl<'a> StructuralEq for Component<'a>[src]

impl<'a> StructuralEq for Prefix<'a>[src]

impl<'a> StructuralEq for PrefixComponent<'a>[src]

impl<T> StructuralEq for TrySendError<T>[src]

impl<T> StructuralEq for Cursor<T>[src]

impl<T> StructuralEq for SendError<T>[src]

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