Trait wasmtime_environ::__core::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 wasmtime_environ::__core::marker::StructuralEq

Background

Implementors§

impl StructuralEq for EntityIndex

impl StructuralEq for FlagValue

impl StructuralEq for GlobalInit

impl StructuralEq for Trap

impl StructuralEq for WasmHeapType

impl StructuralEq for WasmType

impl StructuralEq for BlockType

impl StructuralEq for CanonicalOption

impl StructuralEq for ComponentExternalKind

impl StructuralEq for ComponentOuterAliasKind

impl StructuralEq for ComponentTypeRef

impl StructuralEq for ComponentValType

impl StructuralEq for wasmtime_environ::wasmparser::Encoding

impl StructuralEq for ExternalKind

impl StructuralEq for FrameKind

impl StructuralEq for HeapType

impl StructuralEq for InstantiationArgKind

impl StructuralEq for OuterAliasKind

impl StructuralEq for PrimitiveValType

impl StructuralEq for StorageType

impl StructuralEq for TypeBounds

impl StructuralEq for ValType

impl StructuralEq for AsciiChar

impl StructuralEq for wasmtime_environ::__core::cmp::Ordering

impl StructuralEq for wasmtime_environ::__core::fmt::Alignment

impl StructuralEq for IpAddr

impl StructuralEq for Ipv6MulticastScope

impl StructuralEq for SocketAddr

impl StructuralEq for FpCategory

impl StructuralEq for IntErrorKind

impl StructuralEq for Which

impl StructuralEq for SearchStep

impl StructuralEq for wasmtime_environ::__core::sync::atomic::Ordering

impl StructuralEq for TryReserveErrorKind

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 RecvTimeoutError

impl StructuralEq for TryRecvError

impl StructuralEq for DwarfFileType

impl StructuralEq for Format

impl StructuralEq for gimli::common::SectionId

impl StructuralEq for RunTimeEndian

impl StructuralEq for Pointer

impl StructuralEq for gimli::read::Error

impl StructuralEq for ColumnType

impl StructuralEq for ValueType

impl StructuralEq for gimli::write::cfi::CallFrameInstruction

impl StructuralEq for ConvertError

impl StructuralEq for Address

impl StructuralEq for gimli::write::Error

impl StructuralEq for Reference

impl StructuralEq for LineString

impl StructuralEq for gimli::write::loc::Location

impl StructuralEq for gimli::write::range::Range

impl StructuralEq for gimli::write::unit::AttributeValue

impl StructuralEq for Level

impl StructuralEq for LevelFilter

impl StructuralEq for AddressSize

impl StructuralEq for object::common::Architecture

impl StructuralEq for object::common::BinaryFormat

impl StructuralEq for ComdatKind

impl StructuralEq for FileFlags

impl StructuralEq for RelocationEncoding

impl StructuralEq for RelocationKind

impl StructuralEq for SectionFlags

impl StructuralEq for SectionKind

impl StructuralEq for SegmentFlags

impl StructuralEq for SymbolKind

impl StructuralEq for SymbolScope

impl StructuralEq for object::endian::Endianness

impl StructuralEq for CompressionFormat

impl StructuralEq for FileKind

impl StructuralEq for ObjectKind