Trait Eq

1.55.0 (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.

Implementors§

1.28.0 · Source§

Eq

Trait Eq Copy item path

§Derivable

§How can I implement Eq?

Dyn Compatibility§

Implementors§

impl Eq for shadow_rs::fmt::Alignment

impl Eq for DebugAsHex

impl Eq for Sign

impl Eq for TryReserveErrorKind

impl Eq for AsciiChar

impl Eq for CharCase

impl Eq for core::cmp::Ordering

impl Eq for Infallible

impl Eq for FromBytesWithNulError

impl Eq for Locality

impl Eq for AtomicOrdering

impl Eq for SimdAlign

impl Eq for ErrorKind

impl Eq for IpAddr

impl Eq for Ipv6MulticastScope

impl Eq for SocketAddr

impl Eq for FpCategory

impl Eq for IntErrorKind

impl Eq for GetDisjointMutError

impl Eq for SearchStep

impl Eq for core::sync::atomic::Ordering

impl Eq for BacktraceStatus

impl Eq for VarError

impl Eq for SeekFrom

impl Eq for Shutdown

impl Eq for BacktraceStyle

impl Eq for RecvTimeoutError

impl Eq for TryRecvError

impl Eq for Cfg

impl Eq for CfgExpr

impl Eq for Platform

impl Eq for DependencyKind

impl Eq for Applicability

impl Eq for DiagnosticLevel

impl Eq for CrateType

impl Eq for Edition

impl Eq for TargetKind

impl Eq for ArtifactDebuginfo

impl Eq for Message

impl Eq for AutotagOption

impl Eq for BranchType

impl Eq for ConfigLevel

impl Eq for Delta

impl Eq for DiffFormat

impl Eq for Direction

impl Eq for ErrorClass

impl Eq for ErrorCode

impl Eq for FetchPrune

impl Eq for FileFavor

impl Eq for FileMode

impl Eq for ObjectType

impl Eq for ReferenceType

impl Eq for RepositoryState

impl Eq for ResetType

impl Eq for StashApplyProgress

impl Eq for SubmoduleIgnore

impl Eq for SubmoduleUpdate

impl Eq for PackBuilderStage

impl Eq for TrieType

impl Eq for ExtensionType

impl Eq for CalendarAlgorithm

impl Eq for HijriCalendarAlgorithm

impl Eq for CollationCaseFirst

impl Eq for CollationNumericOrdering

impl Eq for CollationType

impl Eq for CurrencyFormatStyle

impl Eq for EmojiPresentationStyle

impl Eq for FirstDay

impl Eq for HourCycle

impl Eq for LineBreakStyle

impl Eq for LineBreakWordHandling

impl Eq for MeasurementSystem

impl Eq for MeasurementUnitOverride

impl Eq for SentenceBreakSupressions

Trait Eq

§How can I implement `Eq`?