Trait Eq

1.4.0 · 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 TryReserveErrorKind

impl Eq for AsciiChar

impl Eq for core::cmp::Ordering

impl Eq for Infallible

impl Eq for FromBytesWithNulError

impl Eq for core::fmt::Alignment

impl Eq for DebugAsHex

impl Eq for Sign

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 ErrorKind

impl Eq for Shutdown

impl Eq for BacktraceStyle

impl Eq for RecvTimeoutError

impl Eq for TryRecvError

impl Eq for json::error::Error

impl Eq for JsonValue

impl Eq for tpacket_versions

impl Eq for num_bigfloat::defs::Error

impl Eq for RoundingMode

impl Eq for BernoulliError

impl Eq for WeightedError

impl Eq for BigEndian

impl Eq for LittleEndian

impl Eq for bool

impl Eq for char

impl Eq for i8

impl Eq for i16

impl Eq for i32

impl Eq for i64

impl Eq for i128

impl Eq for isize

impl Eq for !

impl Eq for str

impl Eq for u8

impl Eq for u16

impl Eq for u32

impl Eq for u64

impl Eq for u128

impl Eq for ()

impl Eq for usize

impl Eq for BigFloat

impl Eq for ByteString

impl Eq for UnorderedKeyError

impl Eq for TryReserveError

impl Eq for CString

impl Eq for FromVecWithNulError

impl Eq for IntoStringError

impl Eq for NulError

impl Eq for FromUtf8Error

impl Eq for String

impl Eq for Layout

impl Eq for LayoutError

impl Eq for core::alloc::AllocError

impl Eq for TypeId

impl Eq for ByteStr

impl Eq for CharTryFromError

impl Eq for ParseCharError

impl Eq for DecodeUtf16Error

impl Eq for TryFromCharError

impl Eq for CpuidResult

impl Eq for CStr

impl Eq for FromBytesUntilNulError

impl Eq for core::fmt::Error

impl Eq for FormattingOptions

impl Eq for PhantomPinned

Trait Eq

§How can I implement `Eq`?