Trait Eq

1.0.0 · 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 AttributeDiscriminant

impl Eq for Delimiter

impl Eq for VarError

impl Eq for pub_just::fmt::Alignment

impl Eq for DebugAsHex

impl Eq for Sign

impl Eq for pub_just::io::ErrorKind

impl Eq for pub_just::io::SeekFrom

impl Eq for Keyword

impl Eq for ParameterKind

impl Eq for SearchStep

impl Eq for StringDelimiter

impl Eq for TokenKind

impl Eq for UnstableFeature

impl Eq for pub_just::cmp::Ordering

impl Eq for TryReserveErrorKind

impl Eq for AsciiChar

impl Eq for Infallible

impl Eq for FromBytesWithNulError

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 core::sync::atomic::Ordering

impl Eq for BacktraceStatus

impl Eq for Shutdown

impl Eq for BacktraceStyle

impl Eq for RecvTimeoutError

impl Eq for TryRecvError

impl Eq for AhoCorasickKind

impl Eq for aho_corasick::packed::api::MatchKind

impl Eq for aho_corasick::util::error::MatchErrorKind

impl Eq for aho_corasick::util::search::Anchored

impl Eq for aho_corasick::util::search::MatchKind

impl Eq for StartKind

impl Eq for anstyle_parse::state::definitions::Action

impl Eq for anstyle_parse::state::definitions::State

impl Eq for AnsiColor

impl Eq for Color

impl Eq for BigEndian

impl Eq for LittleEndian

impl Eq for Colons

impl Eq for Fixed

impl Eq for Numeric

impl Eq for OffsetPrecision

impl Eq for Pad

impl Eq for ParseErrorKind

impl Eq for SecondsFormat

impl Eq for Month

impl Eq for RoundingError

impl Eq for Weekday

impl Eq for ArgPredicate

impl Eq for ValueHint

impl Eq for ContextKind

impl Eq for ContextValue

impl Eq for clap_builder::error::kind::ErrorKind

impl Eq for ValueSource

impl Eq for clap_builder::util::color::ColorChoice

impl Eq for Shell

impl Eq for colorchoice::ColorChoice

impl Eq for tpacket_versions

impl Eq for fsconfig_command

impl Eq for membarrier_cmd

impl Eq for membarrier_cmd_flag

impl Eq for memmap2::advice::Advice

impl Eq for UncheckedAdvice

impl Eq for nix::errno::consts::Errno

impl Eq for FlockArg

impl Eq for PosixFadviseAdvice

impl Eq for PrctlMCEKillPolicy

impl Eq for SigHandler

impl Eq for SigevNotify

impl Eq for SigmaskHow

Trait Eq

§How can I implement `Eq`?