1.0.0[−][src]Trait nom::lib::std::cmp::PartialEq

[+] Show declaration

[+] Expand attributes
#[lang = "eq"]pub trait PartialEq<Rhs = Self> where
    Rhs: ?Sized, {
[+] Expand attributes
#[must_use]    fn eq(&self, other: &Rhs) -> bool;

[+] Expand attributes
#[must_use]    fn ne(&self, other: &Rhs) -> bool { ... }
}

[−]

Trait for equality comparisons which are partial equivalence relations.

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.

Formally, the equality must be (for all a, b and c):

symmetric: a == b implies b == a; and
transitive: a == b and b == c implies a == c.

Note that these requirements mean that the trait itself must be implemented symmetrically and transitively: if T: PartialEq<U> and U: PartialEq<V> then U: PartialEq<T> and T: PartialEq<V>.

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`?

PartialEq only requires the eq method to be implemented; ne is defined in terms of it by default. Any manual implementation of ne must respect the rule that eq is a strict inverse of ne; that is, !(a == b) if and only if a != b.

Implementations of PartialEq, PartialOrd, and Ord must agree with each other. It's easy to accidentally make them disagree by deriving some of the traits and manually implementing others.

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);

Required methods

`[+] Expand attributes #[must_use]fn eq(&self, other: &Rhs) -> bool`[−]

This method tests for self and other values to be equal, and is used by ==.

Provided methods

`[+] Expand attributes #[must_use]fn ne(&self, other: &Rhs) -> bool`[−]

This method tests for !=.

1.0.0[−][src]Trait nom::lib::std::cmp::PartialEq

Derivable

How can I implement PartialEq?

How can I compare two different types?

Examples

Required methods

[+] Expand attributes#[must_use]fn eq(&self, other: &Rhs) -> bool[−]

Provided methods

[+] Expand attributes#[must_use]fn ne(&self, other: &Rhs) -> bool[−]

Implementations on Foreign Types

impl<'a, 'b> PartialEq<PathBuf> for &'a Path[src][−]

fn eq(&self, other: &PathBuf) -> bool[src]

impl PartialEq<BacktraceStatus> for BacktraceStatus[src][−]

fn eq(&self, other: &BacktraceStatus) -> bool[src]

impl<'a, 'b> PartialEq<Cow<'a, OsStr>> for OsString[src][−]

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

impl PartialEq<SocketAddrV6> for SocketAddrV6[src][−]

fn eq(&self, other: &SocketAddrV6) -> bool[src]

impl<'_> PartialEq<&'_ str> for OsString[src][−]

fn eq(&self, other: &&str) -> bool[src]

impl PartialEq<Permissions> for Permissions[src][−]

fn eq(&self, other: &Permissions) -> bool[src]

fn ne(&self, other: &Permissions) -> bool[src]

impl<'a> PartialEq<Prefix<'a>> for Prefix<'a>[src][−]

fn eq(&self, other: &Prefix<'a>) -> bool[src]

fn ne(&self, other: &Prefix<'a>) -> bool[src]

impl PartialEq<SocketAddrV4> for SocketAddrV4[src][−]

fn eq(&self, other: &SocketAddrV4) -> bool[src]

impl<'a, 'b> PartialEq<&'a Path> for OsString[src][−]

fn eq(&self, other: &&'a Path) -> bool[src]

impl PartialEq<OsStr> for OsStr[src][−]

fn eq(&self, other: &OsStr) -> bool[src]

impl PartialEq<Instant> for Instant[src][−]

fn eq(&self, other: &Instant) -> bool[src]

fn ne(&self, other: &Instant) -> bool[src]

impl<'a> PartialEq<PrefixComponent<'a>> for PrefixComponent<'a>[src][−]

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

impl PartialEq<str> for OsString[src][−]

fn eq(&self, other: &str) -> bool[src]

impl<'a, 'b> PartialEq<Cow<'a, OsStr>> for PathBuf[src][−]

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

impl PartialEq<Ipv6MulticastScope> for Ipv6MulticastScope[src][−]

fn eq(&self, other: &Ipv6MulticastScope) -> bool[src]

impl PartialEq<CString> for CString[src][−]

fn eq(&self, other: &CString) -> bool[src]

fn ne(&self, other: &CString) -> bool[src]

impl PartialEq<IpAddr> for IpAddr[src][−]

fn eq(&self, other: &IpAddr) -> bool[src]

fn ne(&self, other: &IpAddr) -> bool[src]

impl PartialEq<OsString> for OsString[src][−]

fn eq(&self, other: &OsString) -> bool[src]

impl<'a, 'b> PartialEq<&'a OsStr> for OsString[src][−]

fn eq(&self, other: &&'a OsStr) -> bool[src]

impl<'a, 'b> PartialEq<Path> for PathBuf[src][−]

fn eq(&self, other: &Path) -> bool[src]

impl<'a> PartialEq<Components<'a>> for Components<'a>[src][−]

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

impl PartialEq<SystemTime> for SystemTime[src][−]

fn eq(&self, other: &SystemTime) -> bool[src]

fn ne(&self, other: &SystemTime) -> bool[src]

impl<'a, 'b> PartialEq<Cow<'b, OsStr>> for &'a Path[src][−]

fn eq(&self, other: &Cow<'b, OsStr>) -> bool[src]

impl<T> PartialEq<Cursor<T>> for Cursor<T> where T: PartialEq<T>, [src][−]

fn eq(&self, other: &Cursor<T>) -> bool[src]

fn ne(&self, other: &Cursor<T>) -> bool[src]

impl<'a, 'b> PartialEq<&'a Path> for OsStr[src][−]

fn eq(&self, other: &&'a Path) -> bool[src]

impl<'a, 'b> PartialEq<&'a OsStr> for Path[src][−]

fn eq(&self, other: &&'a OsStr) -> bool[src]

impl PartialEq<TryRecvError> for TryRecvError[src][−]

fn eq(&self, other: &TryRecvError) -> bool[src]

impl<T> PartialEq<TrySendError<T>> for TrySendError<T> where T: PartialEq<T>, [src][−]

fn eq(&self, other: &TrySendError<T>) -> bool[src]

fn ne(&self, other: &TrySendError<T>) -> bool[src]

impl<'a, 'b> PartialEq<OsStr> for OsString[src][−]

fn eq(&self, other: &OsStr) -> bool[src]

impl<'a, 'b> PartialEq<OsString> for &'a Path[src][−]

fn eq(&self, other: &OsString) -> bool[src]

impl<'a, 'b> PartialEq<Cow<'a, OsStr>> for &'b OsStr[src][−]

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

How can I implement `PartialEq`?

`[+] Expand attributes #[must_use]fn eq(&self, other: &Rhs) -> bool`[−]

`[+] Expand attributes #[must_use]fn ne(&self, other: &Rhs) -> bool`[−]

`impl<'a, 'b> PartialEq<PathBuf> for &'a Path`[src][−]

`fn eq(&self, other: &PathBuf) -> bool`[src]

`impl PartialEq<BacktraceStatus> for BacktraceStatus`[src][−]

`fn eq(&self, other: &BacktraceStatus) -> bool`[src]

`impl<'a, 'b> PartialEq<Cow<'a, OsStr>> for OsString`[src][−]

`fn eq(&self, other: &Cow<'a, OsStr>) -> bool`[src]

`impl PartialEq<SocketAddrV6> for SocketAddrV6`[src][−]

`fn eq(&self, other: &SocketAddrV6) -> bool`[src]

`impl<'_> PartialEq<&'_ str> for OsString`[src][−]

`fn eq(&self, other: &&str) -> bool`[src]

`impl PartialEq<Permissions> for Permissions`[src][−]

`fn eq(&self, other: &Permissions) -> bool`[src]

`fn ne(&self, other: &Permissions) -> bool`[src]

`impl<'a> PartialEq<Prefix<'a>> for Prefix<'a>`[src][−]

`fn eq(&self, other: &Prefix<'a>) -> bool`[src]

`fn ne(&self, other: &Prefix<'a>) -> bool`[src]

`impl PartialEq<SocketAddrV4> for SocketAddrV4`[src][−]

`fn eq(&self, other: &SocketAddrV4) -> bool`[src]

`impl<'a, 'b> PartialEq<&'a Path> for OsString`[src][−]

`fn eq(&self, other: &&'a Path) -> bool`[src]

`impl PartialEq<OsStr> for OsStr`[src][−]

`fn eq(&self, other: &OsStr) -> bool`[src]

`impl PartialEq<Instant> for Instant`[src][−]

`fn eq(&self, other: &Instant) -> bool`[src]

`fn ne(&self, other: &Instant) -> bool`[src]

`impl<'a> PartialEq<PrefixComponent<'a>> for PrefixComponent<'a>`[src][−]

`fn eq(&self, other: &PrefixComponent<'a>) -> bool`[src]

`impl PartialEq<str> for OsString`[src][−]

`fn eq(&self, other: &str) -> bool`[src]

`impl<'a, 'b> PartialEq<Cow<'a, OsStr>> for PathBuf`[src][−]

`fn eq(&self, other: &Cow<'a, OsStr>) -> bool`[src]

`impl PartialEq<Ipv6MulticastScope> for Ipv6MulticastScope`[src][−]

`fn eq(&self, other: &Ipv6MulticastScope) -> bool`[src]

`impl PartialEq<CString> for CString`[src][−]

`fn eq(&self, other: &CString) -> bool`[src]

`fn ne(&self, other: &CString) -> bool`[src]

`impl PartialEq<IpAddr> for IpAddr`[src][−]

`fn eq(&self, other: &IpAddr) -> bool`[src]

`fn ne(&self, other: &IpAddr) -> bool`[src]

`impl PartialEq<OsString> for OsString`[src][−]

`fn eq(&self, other: &OsString) -> bool`[src]

`impl<'a, 'b> PartialEq<&'a OsStr> for OsString`[src][−]

`fn eq(&self, other: &&'a OsStr) -> bool`[src]

`impl<'a, 'b> PartialEq<Path> for PathBuf`[src][−]

`fn eq(&self, other: &Path) -> bool`[src]

`impl<'a> PartialEq<Components<'a>> for Components<'a>`[src][−]

`fn eq(&self, other: &Components<'a>) -> bool`[src]

`impl PartialEq<SystemTime> for SystemTime`[src][−]

`fn eq(&self, other: &SystemTime) -> bool`[src]

`fn ne(&self, other: &SystemTime) -> bool`[src]

`impl<'a, 'b> PartialEq<Cow<'b, OsStr>> for &'a Path`[src][−]

`fn eq(&self, other: &Cow<'b, OsStr>) -> bool`[src]

`impl<T> PartialEq<Cursor<T>> for Cursor<T> where T: PartialEq<T>,` [src][−]

`fn eq(&self, other: &Cursor<T>) -> bool`[src]

`fn ne(&self, other: &Cursor<T>) -> bool`[src]

`impl<'a, 'b> PartialEq<&'a Path> for OsStr`[src][−]

`fn eq(&self, other: &&'a Path) -> bool`[src]

`impl<'a, 'b> PartialEq<&'a OsStr> for Path`[src][−]

`fn eq(&self, other: &&'a OsStr) -> bool`[src]

`impl PartialEq<TryRecvError> for TryRecvError`[src][−]

`fn eq(&self, other: &TryRecvError) -> bool`[src]

`impl<T> PartialEq<TrySendError<T>> for TrySendError<T> where T: PartialEq<T>,` [src][−]

`fn eq(&self, other: &TrySendError<T>) -> bool`[src]

`fn ne(&self, other: &TrySendError<T>) -> bool`[src]

`impl<'a, 'b> PartialEq<OsStr> for OsString`[src][−]

`fn eq(&self, other: &OsStr) -> bool`[src]

`impl<'a, 'b> PartialEq<OsString> for &'a Path`[src][−]

`fn eq(&self, other: &OsString) -> bool`[src]

`impl<'a, 'b> PartialEq<Cow<'a, OsStr>> for &'b OsStr`[src][−]

`fn eq(&self, other: &Cow<'a, OsStr>) -> bool`[src]

`impl PartialEq<OsString> for str`[src][−]

`fn eq(&self, other: &OsString) -> bool`[src]

`impl PartialEq<OsStr> for str`[src][−]

`fn eq(&self, other: &OsStr) -> bool`[src]

`impl<'a, 'b> PartialEq<Path> for OsString`[src][−]

`fn eq(&self, other: &Path) -> bool`[src]

`impl PartialEq<RecvError> for RecvError`[src][−]