Trait Eq

1.6.0 · Source

pub trait Eq: PartialEq { }

Expand description

Trait for comparisons corresponding to equivalence relations.

The primary difference to PartialEq is the additional requirement for reflexivity. A type that implements PartialEq guarantees that for all a, b and c:

symmetric: a == b implies b == a and a != b implies !(a == b)
transitive: a == b and b == c implies a == c

Eq, which builds on top of PartialEq also implies:

reflexive: a == a

This property cannot be checked by the compiler, and therefore Eq is a trait without methods.

Violating this property is a logic error. The behavior resulting from a logic error is not specified, but users of the trait must ensure that such logic errors do not result in undefined behavior. This means that unsafe code must not rely on the correctness of these methods.

Floating point types such as f32 and f64 implement only PartialEq but not Eq because NaN != NaN.

§Derivable

This trait can be used with #[derive]. When derived, because Eq has no extra methods, it is only informing the compiler that this is an equivalence relation rather than a partial equivalence relation. Note that the derive strategy requires all fields are Eq, which isn’t always desired.

§How can I implement `Eq`?

If you cannot use the derive strategy, specify that your type implements Eq, which has no extra methods:

enum BookFormat {
    Paperback,
    Hardback,
    Ebook,
}

struct Book {
    isbn: i32,
    format: BookFormat,
}

impl PartialEq for Book {
    fn eq(&self, other: &Self) -> bool {
        self.isbn == other.isbn
    }
}

impl Eq for Book {}

Dyn Compatibility§

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Trait EqCopy item path

§Derivable

§How can I implement Eq?

Dyn Compatibility§

Implementors§

impl Eq for wasmtime_environ::component::dfg::CoreDef

impl Eq for Trampoline

impl Eq for wasmtime_environ::component::CoreDef

impl Eq for FixedEncoding

impl Eq for FlatType

impl Eq for InterfaceType

impl Eq for StringEncoding

impl Eq for Transcode

impl Eq for Collector

impl Eq for ConstOp

impl Eq for EngineOrModuleTypeIndex

impl Eq for EntityIndex

impl Eq for IndexType

impl Eq for wasmtime_environ::RelocationTarget

impl Eq for Trap

impl Eq for VMGcKind

impl Eq for WasmCompositeInnerType

impl Eq for WasmHeapBottomType

impl Eq for WasmHeapTopType

impl Eq for WasmHeapType

impl Eq for WasmStorageType

impl Eq for WasmValType

impl Eq for LibCall

impl Eq for AsciiChar

impl Eq for wasmtime_environ::__core::cmp::Ordering

impl Eq for Infallible

impl Eq for wasmtime_environ::__core::fmt::Alignment

impl Eq for IpAddr

impl Eq for Ipv6MulticastScope

impl Eq for SocketAddr

impl Eq for FpCategory

impl Eq for IntErrorKind

impl Eq for SearchStep

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

impl Eq for TryReserveErrorKind

impl Eq for BacktraceStatus

impl Eq for VarError

impl Eq for std::io::SeekFrom

impl Eq for std::io::error::ErrorKind

impl Eq for Shutdown

impl Eq for BacktraceStyle

impl Eq for RecvTimeoutError

impl Eq for TryRecvError

impl Eq for cpp_demangle::ast::ArrayType

impl Eq for BaseUnresolvedName

impl Eq for BuiltinType

impl Eq for CallOffset

impl Eq for ClassEnumType

impl Eq for CtorDtorName

impl Eq for Decltype

impl Eq for DestructorName

impl Eq for cpp_demangle::ast::Encoding

impl Eq for ExceptionSpec

impl Eq for ExprPrimary

impl Eq for cpp_demangle::ast::Expression

impl Eq for GlobalCtorDtor

impl Eq for LocalName

impl Eq for MangledName

impl Eq for Name

impl Eq for NestedName

impl Eq for OperatorName

impl Eq for cpp_demangle::ast::Prefix

impl Eq for PrefixHandle

impl Eq for RefQualifier

impl Eq for SimpleOperatorName

impl Eq for SpecialName

impl Eq for StandardBuiltinType

impl Eq for Substitution

impl Eq for TemplateArg

impl Eq for TemplateTemplateParamHandle

impl Eq for Type

impl Eq for TypeHandle

impl Eq for UnqualifiedName

impl Eq for UnresolvedName

impl Eq for UnresolvedType

Trait Eq

§How can I implement `Eq`?