rustmax::static_assertions::_core::prelude::rust_2024

Trait Eq

pub trait Eq: PartialEq { }

🔬This is a nightly-only experimental API. (prelude_2024)

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 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 Action

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

impl Eq for CChar

impl Eq for cexpr::token::Kind

impl Eq for Tz

impl Eq for clang_sys::Version

impl Eq for LabelStyle

impl Eq for Severity

impl Eq for colorchoice::ColorChoice

impl Eq for CoderResult

impl Eq for DecoderResult

impl Eq for EncoderResult

impl Eq for Latin1Bidi

impl Eq for DwarfFileType

impl Eq for Format

impl Eq for SectionId

impl Eq for Vendor

impl Eq for RunTimeEndian

impl Eq for AbbreviationsCacheStrategy

impl Eq for Pointer

impl Eq for gimli::read::Error

impl Eq for IndexSectionId

impl Eq for ColumnType

impl Eq for ValueType

impl Eq for globset::ErrorKind

impl Eq for hashbrown::TryReserveError

impl Eq for AdditionError

impl Eq for CreationError

impl Eq for RecordError

impl Eq for SubtractionError

impl Eq for httparse::Error

impl Eq for Kilo

impl Eq for TrieType

impl Eq for ExtensionType

impl Eq for icu_locid_transform::directionality::Direction

impl Eq for Decomposed

impl Eq for BidiPairingProperties

impl Eq for PropertiesError

impl Eq for GeneralCategory

impl Eq for CheckedBidiPairedBracketType

impl Eq for BufferFormat

impl Eq for DataErrorKind

impl Eq for LocaleFallbackPriority

impl Eq for LocaleFallbackSupplement

impl Eq for DnsLength

impl Eq for ErrorPolicy

impl Eq for Hyphens

impl Eq for ProcessingError

impl Eq for ProcessingSuccess

impl Eq for WalkState

impl Eq for IpAddrRange

impl Eq for IpNet

impl Eq for IpSubnets

impl Eq for itertools::with_position::Position

impl Eq for fsconfig_command

impl Eq for membarrier_cmd

impl Eq for membarrier_cmd_flag

impl Eq for InsertError

impl Eq for matchit::error::MatchError

impl Eq for DataFormat

impl Eq for MZError

impl Eq for MZFlush

impl Eq for MZStatus

impl Eq for TINFLStatus

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

impl Eq for FlockArg

impl Eq for PosixFadviseAdvice

impl Eq for PrctlMCEKillPolicy

impl Eq for SigHandler

Trait Eq

§How can I implement `Eq`?