Trait nom::lib::std::prelude::v1::rust_2015::PartialEq1.0.0[−][src]

pub trait PartialEq<Rhs = Self> where
    Rhs: ?Sized, {
    fn eq(&self, other: &Rhs) -> bool;

    fn ne(&self, other: &Rhs) -> bool { ... }
}

Expand description

Trait for equality comparisons which are partial equivalence relations.

x.eq(y) can also be written x == y, and x.ne(y) can be written x != y. We use the easier-to-read infix notation in the remainder of this documentation.

This trait allows for partial equality, for types that do not have a full equivalence relation. For example, in floating point numbers NaN != NaN, so floating point types implement PartialEq but not Eq.

Implementations must ensure that eq and ne are consistent with each other:

a != b if and only if !(a == b) (ensured by the default implementation).

If PartialOrd or Ord are also implemented for Self and Rhs, their methods must also be consistent with PartialEq (see the documentation of those traits for the exact requirements). It’s easy to accidentally make them disagree by deriving some of the traits and manually implementing others.

The equality relation == must satisfy the following conditions (for all a, b, c of type A, B, C):

Symmetric: if A: PartialEq and B: PartialEq<A>, then a == b implies b == a; and
Transitive: if A: PartialEq and B: PartialEq<C> and A: PartialEq<C>, then a == b and b == c implies a == c.

Note that the B: PartialEq<A> (symmetric) and A: PartialEq<C> (transitive) impls are not forced to exist, but these requirements apply whenever they do exist.

Derivable

This trait can be used with #[derive]. When derived on structs, two instances are equal if all fields are equal, and not equal if any fields are not equal. When derived on enums, each variant is equal to itself and not equal to the other variants.

How can I implement `PartialEq`?

An example implementation for a domain in which two books are considered the same book if their ISBN matches, even if the formats differ:

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
    }
}

let b1 = Book { isbn: 3, format: BookFormat::Paperback };
let b2 = Book { isbn: 3, format: BookFormat::Ebook };
let b3 = Book { isbn: 10, format: BookFormat::Paperback };

assert!(b1 == b2);
assert!(b1 != b3);

How can I compare two different types?

The type you can compare with is controlled by PartialEq’s type parameter. For example, let’s tweak our previous code a bit:

// The derive implements <BookFormat> == <BookFormat> comparisons
#[derive(PartialEq)]
enum BookFormat {
    Paperback,
    Hardback,
    Ebook,
}

struct Book {
    isbn: i32,
    format: BookFormat,
}

// Implement <Book> == <BookFormat> comparisons
impl PartialEq<BookFormat> for Book {
    fn eq(&self, other: &BookFormat) -> bool {
        self.format == *other
    }
}

// Implement <BookFormat> == <Book> comparisons
impl PartialEq<Book> for BookFormat {
    fn eq(&self, other: &Book) -> bool {
        *self == other.format
    }
}

let b1 = Book { isbn: 3, format: BookFormat::Paperback };

assert!(b1 == BookFormat::Paperback);
assert!(BookFormat::Ebook != b1);

By changing impl PartialEq for Book to impl PartialEq<BookFormat> for Book, we allow BookFormats to be compared with Books.

A comparison like the one above, which ignores some fields of the struct, can be dangerous. It can easily lead to an unintended violation of the requirements for a partial equivalence relation. For example, if we kept the above implementation of PartialEq<Book> for BookFormat and added an implementation of PartialEq<Book> for Book (either via a #[derive] or via the manual implementation from the first example) then the result would violate transitivity:

#[derive(PartialEq)]
enum BookFormat {
    Paperback,
    Hardback,
    Ebook,
}

#[derive(PartialEq)]
struct Book {
    isbn: i32,
    format: BookFormat,
}

impl PartialEq<BookFormat> for Book {
    fn eq(&self, other: &BookFormat) -> bool {
        self.format == *other
    }
}

impl PartialEq<Book> for BookFormat {
    fn eq(&self, other: &Book) -> bool {
        *self == other.format
    }
}

fn main() {
    let b1 = Book { isbn: 1, format: BookFormat::Paperback };
    let b2 = Book { isbn: 2, format: BookFormat::Paperback };

    assert!(b1 == BookFormat::Paperback);
    assert!(BookFormat::Paperback == b2);

    // The following should hold by transitivity but doesn't.
    assert!(b1 == b2); // <-- PANICS
}

Examples

let x: u32 = 0;
let y: u32 = 1;

assert_eq!(x == y, false);
assert_eq!(x.eq(&y), false);

Trait nom::lib::std::prelude::v1::rust_2015::PartialEq1.0.0[−][src]

Required methods

fn eq(&self, other: &Rhs) -> bool

Provided methods

fn ne(&self, other: &Rhs) -> bool

Implementations on Foreign Types

impl<'a, 'b> PartialEq<Cow<'a, OsStr>> for &'b OsStr

pub fn eq(&self, other: &Cow<'a, OsStr>) -> bool

impl<'a> PartialEq<PrefixComponent<'a>> for PrefixComponent<'a>

pub fn eq(&self, other: &PrefixComponent<'a>) -> bool

impl PartialEq<AccessError> for AccessError

pub fn eq(&self, other: &AccessError) -> bool

impl<'a, 'b> PartialEq<PathBuf> for &'a OsStr

pub fn eq(&self, other: &PathBuf) -> bool

impl<'a, 'b> PartialEq<OsStr> for PathBuf

pub fn eq(&self, other: &OsStr) -> bool

impl PartialEq<OsString> for str

pub fn eq(&self, other: &OsString) -> bool

impl PartialEq<CStr> for CStr

pub fn eq(&self, other: &CStr) -> bool

impl PartialEq<FromVecWithNulError> for FromVecWithNulError

pub fn eq(&self, other: &FromVecWithNulError) -> bool

pub fn ne(&self, other: &FromVecWithNulError) -> bool

impl<'a, 'b> PartialEq<&'a OsStr> for Path

pub fn eq(&self, other: &&'a OsStr) -> bool

impl<T> PartialEq<Cursor<T>> for Cursor<T> where T: PartialEq<T>,

pub fn eq(&self, other: &Cursor<T>) -> bool

pub fn ne(&self, other: &Cursor<T>) -> bool

impl PartialEq<OsStr> for str

pub fn eq(&self, other: &OsStr) -> bool

impl<T> PartialEq<TrySendError<T>> for TrySendError<T> where T: PartialEq<T>,

pub fn eq(&self, other: &TrySendError<T>) -> bool

pub fn ne(&self, other: &TrySendError<T>) -> bool

impl PartialEq<StripPrefixError> for StripPrefixError

pub fn eq(&self, other: &StripPrefixError) -> bool

pub fn ne(&self, other: &StripPrefixError) -> bool

impl PartialEq<Shutdown> for Shutdown

pub fn eq(&self, other: &Shutdown) -> bool

impl PartialEq<SeekFrom> for SeekFrom

pub fn eq(&self, other: &SeekFrom) -> bool

pub fn ne(&self, other: &SeekFrom) -> bool

impl PartialEq<PathBuf> for PathBuf

pub fn eq(&self, other: &PathBuf) -> bool

impl<'a, 'b> PartialEq<Path> for &'a OsStr

pub fn eq(&self, other: &Path) -> bool

impl<'a, 'b> PartialEq<Cow<'a, OsStr>> for Path

pub fn eq(&self, other: &Cow<'a, OsStr>) -> bool

impl<T> PartialEq<SendError<T>> for SendError<T> where T: PartialEq<T>,

pub fn eq(&self, other: &SendError<T>) -> bool

pub fn ne(&self, other: &SendError<T>) -> bool

impl PartialEq<NulError> for NulError

pub fn eq(&self, other: &NulError) -> bool

pub fn ne(&self, other: &NulError) -> bool

impl<'a, 'b> PartialEq<OsStr> for OsString

pub fn eq(&self, other: &OsStr) -> bool

impl PartialEq<Ipv6Addr> for IpAddr

pub fn eq(&self, other: &Ipv6Addr) -> bool

impl PartialEq<IpAddr> for Ipv6Addr

pub fn eq(&self, other: &IpAddr) -> bool

impl PartialEq<SocketAddrV4> for SocketAddrV4

pub fn eq(&self, other: &SocketAddrV4) -> bool

impl PartialEq<ExitStatusError> for ExitStatusError

pub fn eq(&self, other: &ExitStatusError) -> bool

pub fn ne(&self, other: &ExitStatusError) -> bool

impl<'a, 'b> PartialEq<&'a Path> for OsString

pub fn eq(&self, other: &&'a Path) -> bool

impl<'a, 'b> PartialEq<OsString> for OsStr

pub fn eq(&self, other: &OsString) -> bool

impl PartialEq<IntoStringError> for IntoStringError

pub fn eq(&self, other: &IntoStringError) -> bool

pub fn ne(&self, other: &IntoStringError) -> bool

impl<'_> PartialEq<&'_ str> for OsString

pub fn eq(&self, other: &&str) -> bool

impl<'a> PartialEq<Components<'a>> for Components<'a>

pub fn eq(&self, other: &Components<'a>) -> bool

impl PartialEq<Instant> for Instant

pub fn eq(&self, other: &Instant) -> bool

pub fn ne(&self, other: &Instant) -> bool

impl PartialEq<CString> for CString

pub fn eq(&self, other: &CString) -> bool

impl<T> PartialEq<Cursor<T>> for Cursor<T> where
T: PartialEq<T>,

impl<T> PartialEq<TrySendError<T>> for TrySendError<T> where
T: PartialEq<T>,

impl<T> PartialEq<SendError<T>> for SendError<T> where
T: PartialEq<T>,

impl<T> PartialEq<SyncOnceCell<T>> for SyncOnceCell<T> where
T: PartialEq<T>,