Trait wasmer_types::lib::std::marker::StructuralEq

source ·

pub trait StructuralEq { }

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

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);

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.

Trait wasmer_types::lib::std::marker::StructuralEq

Background

Implementors§

impl StructuralEq for ExportIndex

impl StructuralEq for ExternType

impl StructuralEq for ImportIndex

impl StructuralEq for Mutability

impl StructuralEq for Type

impl StructuralEq for wasmer_types::lib::std::cmp::Ordering

impl StructuralEq for wasmer_types::lib::std::fmt::Alignment

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

impl StructuralEq for RecvTimeoutError

impl StructuralEq for TryRecvError

impl StructuralEq for TryReserveErrorKind

impl StructuralEq for AsciiChar

impl StructuralEq for Which

impl StructuralEq for IpAddr

impl StructuralEq for Ipv6MulticastScope

impl StructuralEq for SocketAddr

impl StructuralEq for FpCategory

impl StructuralEq for IntErrorKind

impl StructuralEq for SearchStep

impl StructuralEq for BacktraceStatus

impl StructuralEq for VarError

impl StructuralEq for SeekFrom

impl StructuralEq for ErrorKind

impl StructuralEq for Shutdown

impl StructuralEq for BacktraceStyle

impl StructuralEq for ArchivedIpAddr

impl StructuralEq for ArchivedSocketAddr

impl StructuralEq for OffsetError

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 ()

impl StructuralEq for usize

impl StructuralEq for Bytes

impl StructuralEq for CustomSectionIndex

impl StructuralEq for DataIndex

impl StructuralEq for DataInitializerLocation

impl StructuralEq for ElemIndex

impl StructuralEq for ExternRef

impl StructuralEq for FastGasCounter

impl StructuralEq for Features

impl StructuralEq for FunctionIndex

impl StructuralEq for FunctionType

impl StructuralEq for GlobalIndex

impl StructuralEq for GlobalType

impl StructuralEq for ImportCounts

impl StructuralEq for LocalFunctionIndex

impl StructuralEq for LocalGlobalIndex

impl StructuralEq for LocalMemoryIndex

impl StructuralEq for LocalTableIndex

impl StructuralEq for MemoryIndex

impl StructuralEq for MemoryType

impl StructuralEq for OwnedDataInitializer

impl StructuralEq for OwnedTableInitializer

impl StructuralEq for Pages

impl StructuralEq for SignatureIndex

impl StructuralEq for TableIndex

impl StructuralEq for TableType

impl StructuralEq for V128

impl StructuralEq for VMExternRef

impl StructuralEq for TypeId

impl StructuralEq for wasmer_types::lib::std::fmt::Error

impl StructuralEq for Assume

impl StructuralEq for RangeFull

impl StructuralEq for wasmer_types::lib::std::ptr::Alignment

impl StructuralEq for FromUtf8Error