Trait Eq

1.0.0 (const: unstable) · 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.

Eq

Trait Eq Copy item path

§Derivable

§How can I implement Eq?

Dyn Compatibility§

Implementors§

impl Eq for hashbrown::TryReserveError

impl Eq for indexmap::GetDisjointMutError

impl Eq for proc_macro2::Spacing

impl Eq for FoundCrate

impl Eq for AttrStyle

impl Eq for Meta

impl Eq for Fields

impl Eq for Data

impl Eq for Expr

impl Eq for Member

impl Eq for PointerMutability

impl Eq for RangeLimits

impl Eq for CapturedParam

impl Eq for GenericParam

impl Eq for TraitBoundModifier

impl Eq for TypeParamBound

impl Eq for WherePredicate

impl Eq for FnArg

impl Eq for ForeignItem

impl Eq for ImplItem

impl Eq for ImplRestriction

impl Eq for Item

impl Eq for StaticMutability

impl Eq for TraitItem

impl Eq for UseTree

impl Eq for Lit

impl Eq for MacroDelimiter

impl Eq for BinOp

impl Eq for UnOp

impl Eq for Pat

impl Eq for GenericArgument

impl Eq for PathArguments

impl Eq for FieldMutability

impl Eq for Visibility

impl Eq for Stmt

impl Eq for ReturnType

impl Eq for syn::ty::Type

impl Eq for Offset

impl Eq for Encoding

impl Eq for IntegerRadix

impl Eq for ScalarKind

impl Eq for Expected

impl Eq for TokenKind

impl Eq for EventKind

impl Eq for Endianness

impl Eq for Needed

impl Eq for StrContext

impl Eq for StrContextValue

impl Eq for CompareResult

impl Eq for Equality

impl Eq for Target

impl Eq for Scope

impl Eq for SuppliedScope

impl Eq for UsageMode

impl Eq for ExpectedDriverKind

impl Eq for RepeatOver

impl Eq for OrigDollarHandledDiscriminants

impl Eq for Grouping

impl Eq for derive_deftly_macros::prelude::Delimiter

impl Eq for derive_deftly_macros::prelude::fmt::Alignment

impl Eq for DebugAsHex

impl Eq for Sign

impl Eq for derive_deftly_macros::prelude::cmp::Ordering

impl Eq for TryReserveErrorKind

impl Eq for AsciiChar

impl Eq for Infallible

impl Eq for FromBytesWithNulError

impl Eq for AtomicOrdering

impl Eq for SimdAlign

impl Eq for IpAddr

impl Eq for Ipv6MulticastScope

impl Eq for SocketAddr

impl Eq for FpCategory

impl Eq for IntErrorKind

Trait Eq

§How can I implement `Eq`?