std::cmp

Trait Eq

pub trait Eq: PartialEq {
    // Provided methods
    #[doc(hidden)]
    fn assert_receiver_is_total_eq(&self) { ... }
    #[doc(hidden)]
    fn assert_fields_are_eq(&self) { ... }
}

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
transitive: a == b and b == c implies a == c
consistent: a != b if and only if !(a == b)

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 {}

Provided Methods§

1.0.0 (const: unstable) · Source

#[doc(hidden)]
fn assert_receiver_is_total_eq(&self)

👎Deprecated since 1.95.0:

implementation detail of #[derive(Eq)]

Source

#[doc(hidden)]
fn assert_fields_are_eq(&self)

🔬This is a nightly-only experimental API. (derive_eq_internals)

Dyn Compatibility§

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Eq

Trait Eq Copy item path

§Derivable

§How can I implement Eq?

Provided Methods§

#[doc(hidden)]fn assert_receiver_is_total_eq(&self)

#[doc(hidden)]fn assert_fields_are_eq(&self)

Dyn Compatibility§

Implementors§

impl Eq for !

impl Eq for ()

impl Eq for AccessError

impl Eq for AddrParseError

impl Eq for std::mem::Alignment

impl Eq for std::fmt::Alignment

impl Eq for AllocError

impl Eq for AsciiChar

impl Eq for Assume

impl Eq for AtomicOrdering

impl Eq for BacktraceStatus

impl Eq for BacktraceStyle

impl Eq for Big8x3

impl Eq for Big32x40

impl Eq for ByteStr

impl Eq for ByteString

impl Eq for CStr

impl Eq for CString

impl Eq for CharCase

impl Eq for CharTryFromError

impl Eq for CodePoint

impl Eq for CodePointInner

impl Eq for Components<'_>

impl Eq for CpuidResult

impl Eq for DebugAsHex

impl Eq for Decimal

impl Eq for DecodeUtf16Error

impl Eq for Decoded

impl Eq for Duration

impl Eq for Error

impl Eq for ErrorKind

impl Eq for ExitCode

impl Eq for std::process::ExitStatus

impl Eq for std::sys::process::unix::unix::ExitStatus

impl Eq for std::process::ExitStatusError

impl Eq for std::sys::process::unix::unix::ExitStatusError

impl Eq for FieldId

impl Eq for FilePermissions

impl Eq for std::fs::FileType

impl Eq for std::sys::fs::unix::FileType

impl Eq for FormattingOptions

impl Eq for FpCategory

impl Eq for FromBytesUntilNulError

impl Eq for FromBytesWithNulError

impl Eq for FromUtf8Error

impl Eq for FromVecWithNulError

impl Eq for FullDecoded

impl Eq for GetDisjointMutError

impl Eq for I32NotAllOnes

impl Eq for I64NotAllOnes

impl Eq for Infallible

impl Eq for std::time::Instant

impl Eq for std::sys::time::unix::Instant

impl Eq for IntErrorKind

impl Eq for IntoStringError

impl Eq for IpAddr

impl Eq for Ipv4Addr

impl Eq for Ipv6Addr

impl Eq for Ipv6MulticastScope

impl Eq for Layout

impl Eq for LayoutError

impl Eq for Locality

impl Eq for Location<'_>

impl Eq for MapsEntry

impl Eq for Nanoseconds

impl Eq for NonZeroCharInner

impl Eq for NonZeroI8Inner

impl Eq for NonZeroI16Inner

impl Eq for NonZeroI32Inner

impl Eq for NonZeroI64Inner

impl Eq for NonZeroI128Inner

Trait Eq

§How can I implement `Eq`?

#[doc(hidden)]
fn assert_receiver_is_total_eq(&self)

#[doc(hidden)]
fn assert_fields_are_eq(&self)