Trait cairo_vm::with_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);

#[allow(pointer_structural_match)]
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 cairo_vm::with_std::marker::StructuralEq

Background

Implementors§

impl StructuralEq for Dictionary

impl StructuralEq for BuiltinName

impl StructuralEq for OffsetValue

impl StructuralEq for ApUpdate

impl StructuralEq for FpUpdate

impl StructuralEq for Op1Addr

impl StructuralEq for Opcode

impl StructuralEq for PcUpdate

impl StructuralEq for Register

impl StructuralEq for Res

impl StructuralEq for MaybeRelocatable

impl StructuralEq for ExecScopeError

impl StructuralEq for InsufficientAllocatedCellsError

impl StructuralEq for BuiltinAdditionalData

impl StructuralEq for CairoArg

impl StructuralEq for cairo_vm::with_std::cmp::Ordering

impl StructuralEq for cairo_vm::with_std::fmt::Alignment

impl StructuralEq for FpCategory

impl StructuralEq for IntErrorKind

impl StructuralEq for SearchStep

impl StructuralEq for cairo_vm::with_std::sync::atomic::Ordering

impl StructuralEq for RecvTimeoutError

impl StructuralEq for TryRecvError

impl StructuralEq for TryReserveErrorKind

impl StructuralEq for AsciiChar

impl StructuralEq for IpAddr

impl StructuralEq for Ipv6MulticastScope

impl StructuralEq for SocketAddr

impl StructuralEq for BacktraceStatus

impl StructuralEq for VarError

impl StructuralEq for SeekFrom

impl StructuralEq for std::io::error::ErrorKind

impl StructuralEq for Shutdown

impl StructuralEq for BacktraceStyle

impl StructuralEq for AllowedEnumVariants

impl StructuralEq for IntegerType

impl StructuralEq for hashbrown::TryReserveError

impl StructuralEq for nom::error::ErrorKind

impl StructuralEq for Needed

impl StructuralEq for Endianness

impl StructuralEq for Sign

impl StructuralEq for BernoulliError

impl StructuralEq for WeightedError

impl StructuralEq for Category

impl StructuralEq for Value

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 DictManager

impl StructuralEq for DictTracker

impl StructuralEq for HintReference

impl StructuralEq for ApTracking

impl StructuralEq for Attribute

impl StructuralEq for DebugInfo

impl StructuralEq for FlowTrackingData

impl StructuralEq for HintLocation

impl StructuralEq for HintParams

impl StructuralEq for Identifier

impl StructuralEq for InputFile

impl StructuralEq for InstructionLocation

impl StructuralEq for cairo_vm::serde::deserialize_program::Location

impl StructuralEq for Member

impl StructuralEq for Reference

impl StructuralEq for ReferenceManager