Trait Eq

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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 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 PrintFmt

impl Eq for base64::alphabet::ParseAlphabetError

impl Eq for base64::alphabet::ParseAlphabetError

impl Eq for base64::decode::DecodeError

impl Eq for base64::decode::DecodeError

impl Eq for base64::decode::DecodeSliceError

impl Eq for base64::decode::DecodeSliceError

impl Eq for base64::encode::EncodeSliceError

impl Eq for base64::encode::EncodeSliceError

impl Eq for base64::engine::DecodePaddingMode

impl Eq for base64::engine::DecodePaddingMode

impl Eq for CheckedCastError

impl Eq for PodCastError

impl Eq for byteorder::BigEndian

impl Eq for byteorder::LittleEndian

impl Eq for Keviyah

impl Eq for StartOfYear

impl Eq for YearType

impl Eq for Color

impl Eq for Styles

impl Eq for CheckResult

impl Eq for Destination

impl Eq for HashAlgorithm

impl Eq for Initiator

impl Eq for InlineCheckType

impl Eq for MatchResult

impl Eq for ParserMetadata

impl Eq for PolicyDisposition

impl Eq for PolicySource

impl Eq for SubresourceIntegrityMetadata

impl Eq for Violates

impl Eq for cookie::draft::SameSite

impl Eq for cookie::expiration::Expiration

impl Eq for cookie::expiration::Expiration

impl Eq for cookie::parse::ParseError

impl Eq for cookie::parse::ParseError

impl Eq for cookie::same_site::SameSite

impl Eq for crossbeam_channel::err::RecvTimeoutError

impl Eq for crossbeam_channel::err::TryRecvError

impl Eq for PredefinedColorSpace

impl Eq for TokenSerializationType

impl Eq for AnimationState

impl Eq for embedder_traits::Cursor

impl Eq for LoadStatus

impl Eq for MediaSessionActionType

impl Eq for Theme

impl Eq for CoderResult

impl Eq for DecoderResult

impl Eq for EncoderResult

impl Eq for Latin1Bidi

impl Eq for Blocks

impl Eq for RoundingMode

impl Eq for BlockType

impl Eq for EnvironmentMap

impl Eq for LevelMode

impl Eq for LineOrder

impl Eq for SampleType

impl Eq for BlockDescription

impl Eq for RoundingIncrement

impl Eq for fixed_decimal::decimal::Sign

impl Eq for SignDisplay

impl Eq for FlushCompress

impl Eq for FlushDecompress

impl Eq for flate2::mem::Status

impl Eq for Meaning

impl Eq for PollNext

impl Eq for Block

impl Eq for DisposalMethod

impl Eq for Extension

Trait Eq

§How can I implement `Eq`?