Trait std::cmp::Eq

1.0.0 · source ·

pub trait Eq: PartialEq { }

Expand description

Trait for comparisons corresponding to equivalence relations.

This means, that in addition to a == b and a != b being strict inverses, the relation must be (for all a, b and c):

reflexive: a == a;
symmetric: a == b implies b == a (required by PartialEq as well); and
transitive: a == b and b == c implies a == c (required by PartialEq as well).

This property cannot be checked by the compiler, and therefore Eq implies PartialEq, and has no extra 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.

Implement Eq in addition to PartialEq if it’s guaranteed that PartialEq::eq(a, a) always returns true (reflexivity), in addition to the symmetric and transitive properties already required by PartialEq.

§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 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 {}

Run

Object Safety§

This trait is not object safe.

Trait std::cmp::Eq

§Derivable

§How can I implement Eq?

Object Safety§

Implementors§

impl Eq for AsciiChar

impl Eq for BacktraceStatus

impl Eq for TryReserveErrorKind

impl Eq for Infallible

impl Eq for VarError

impl Eq for std::fmt::Alignment

impl Eq for ErrorKind

impl Eq for SeekFrom

impl Eq for IpAddr

impl Eq for Ipv6MulticastScope

impl Eq for Shutdown

impl Eq for SocketAddr

impl Eq for FpCategory

impl Eq for IntErrorKind

impl Eq for BacktraceStyle

impl Eq for SearchStep

impl Eq for std::sync::atomic::Ordering

impl Eq for RecvTimeoutError

impl Eq for TryRecvError

impl Eq for std::cmp::Ordering

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 ColumnType

impl Eq for ValueType

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 CpuidResult

impl Eq for AllocError

impl Eq for Layout

impl Eq for LayoutError

impl Eq for TypeId

impl Eq for CharTryFromError

impl Eq for DecodeUtf16Error

impl Eq for ParseCharError

impl Eq for TryFromCharError

impl Eq for UnorderedKeyError

impl Eq for TryReserveError

impl Eq for FromBytesUntilNulError

impl Eq for FromBytesWithNulError

impl Eq for FromVecWithNulError

impl Eq for IntoStringError

impl Eq for NulError

impl Eq for CStr

impl Eq for CString

impl Eq for OsStr

impl Eq for OsString

impl Eq for std::fmt::Error

impl Eq for FileType

impl Eq for Permissions

impl Eq for PhantomPinned

impl Eq for Assume

impl Eq for AddrParseError

impl Eq for Ipv4Addr

impl Eq for Ipv6Addr

§How can I implement `Eq`?