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 RelocationKind

impl StructuralEq for RelocationTarget

impl StructuralEq for CustomSectionProtection

impl StructuralEq for Symbol

impl StructuralEq for CompiledFunctionUnwindInfo

impl StructuralEq for Aarch64Architecture

impl StructuralEq for Architecture

impl StructuralEq for BinaryFormat

impl StructuralEq for CallingConvention

impl StructuralEq for Endianness

impl StructuralEq for Environment

impl StructuralEq for ExportIndex

impl StructuralEq for ExternType

impl StructuralEq for ImportIndex

impl StructuralEq for LibCall

impl StructuralEq for MemoryStyle

impl StructuralEq for Mutability

impl StructuralEq for OperatingSystem

impl StructuralEq for PointerWidth

impl StructuralEq for TableStyle

impl StructuralEq for TrapCode

impl StructuralEq for Type

impl StructuralEq for Vendor

impl StructuralEq for MemoryError

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 CDataModel

impl StructuralEq for Size

impl StructuralEq for ParseError

impl StructuralEq for ArmArchitecture

impl StructuralEq for CustomVendor

impl StructuralEq for Mips32Architecture

impl StructuralEq for Mips64Architecture

impl StructuralEq for Riscv32Architecture

impl StructuralEq for Riscv64Architecture

impl StructuralEq for X86_32Architecture

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 FunctionAddressMap

impl StructuralEq for InstructionAddressMap

impl StructuralEq for Compilation

impl StructuralEq for CompiledFunction