rama::crypto::dep::x509_parser::prelude::asn1_rs::nom::lib::std::cmp

Trait PartialEq

1.0.0 · Source

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

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

Expand description

Trait for comparisons using the equality operator.

Implementing this trait for types provides the == and != operators for those types.

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 comparisons using the equality operator, 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 speaking, when Rhs == Self, this trait corresponds to a partial equivalence relation.

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

a != b if and only if !(a == b).

The default implementation of ne provides this consistency and is almost always sufficient. It should not be overridden without very good reason.

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):

Symmetry: if A: PartialEq and B: PartialEq<A>, then a == b implies b == a; and
Transitivity: if A: PartialEq and B: PartialEq<C> and A: PartialEq<C>, then a == b and b == c implies a == c. This must also work for longer chains, such as when A: PartialEq, B: PartialEq<C>, C: PartialEq<D>, and A: PartialEq<D> all exist.

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.

Violating these requirements 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.

§Cross-crate considerations

Upholding the requirements stated above can become tricky when one crate implements PartialEq for a type of another crate (i.e., to allow comparing one of its own types with a type from the standard library). The recommendation is to never implement this trait for a foreign type. In other words, such a crate should do impl PartialEq<ForeignType> for LocalType, but it should not do impl PartialEq<LocalType> for ForeignType.

This avoids the problem of transitive chains that criss-cross crate boundaries: for all local types T, you may assume that no other crate will add impls that allow comparing T == U. In other words, if other crates add impls that allow building longer transitive chains U1 == ... == T == V1 == ..., then all the types that appear to the right of T must be types that the crate defining T already knows about. This rules out transitive chains where downstream crates can add new impls that “stitch together” comparisons of foreign types in ways that violate transitivity.

Not having such foreign impls also avoids forward compatibility issues where one crate adding more PartialEq implementations can cause build failures in downstream crates.

§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, two instances are equal if they are the same variant and all fields are equal.

§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);

impl PartialEq for Less

Source §

impl PartialEq for UTerm

Source §

impl PartialEq for OpaqueOrigin

Source §

impl PartialEq for Url

URLs compare like their serialization.

let authority: Authority = "HELLO.com".parse().unwrap();
assert_eq!(authority, "hello.coM");
assert_eq!("hello.com", authority);

Case-insensitive equality

§Examples

let scheme: Scheme = "HTTP".parse().unwrap();
assert_eq!(scheme, *"http");

Case-insensitive equality

impl<T> PartialEq for *mut T
where T: ?Sized,

Pointer equality is by address, as produced by the <*mut T>::addr method.

1.0.0 · Source§

impl<T> PartialEq for (T₁, T₂, …, Tₙ)
where T: PartialEq + ?Sized,

impl<const N: usize> PartialEq<TinyAsciiStr<N>> for String

Source §

impl<const N: usize> PartialEq<[u8; N]> for ByteString

Source §

Trait PartialEqCopy item path

§Cross-crate considerations

§Derivable

§How can I implement PartialEq?

§How can I compare two different types?

§Examples

Required Methods§

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

Provided Methods§

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

Implementors§

impl PartialEq for ForwardKind

impl PartialEq for LookupIpStrategy

impl PartialEq for ResolveHosts

impl PartialEq for ServerOrderingStrategy

impl PartialEq for rama::futures::io::ErrorKind

impl PartialEq for SeekFrom

impl PartialEq for PollNext

impl PartialEq for rama::http::headers::encoding::Encoding

impl PartialEq for After

impl PartialEq for ClientHint

impl PartialEq for Extension

impl PartialEq for PerMessageDeflateIdentifier

impl PartialEq for rama::http::layer::compression::CompressionLevel

impl PartialEq for WriterMode

impl PartialEq for rama::http::matcher::uri::dep::regex::Error

impl PartialEq for PseudoHeader

impl PartialEq for EarlyFrame

impl PartialEq for rama::http::proto::h2::frame::Error

impl PartialEq for rama::http::proto::h2::frame::Kind

impl PartialEq for SettingId

impl PartialEq for DecoderError

impl PartialEq for NeedMore

impl PartialEq for DirectoryServeMode

impl PartialEq for ElementPatchMode

impl PartialEq for EventType

impl PartialEq for CrossOriginKind

impl PartialEq for rama::http::sse::datastar::execute_script::ReferrerPolicy

impl PartialEq for ScriptAttribute

impl PartialEq for ScriptType

impl PartialEq for rama::http::ws::Message

impl PartialEq for Role

impl PartialEq for CloseCode

impl PartialEq for rama::http::ws::protocol::frame::coding::OpCode

impl PartialEq for OpCodeControl

impl PartialEq for OpCodeData

impl PartialEq for rama::net::address::Host

impl PartialEq for ConnectIpMode

impl PartialEq for DnsResolveIpMode

impl PartialEq for rama::net::socket::opts::Domain

impl PartialEq for rama::net::socket::opts::Protocol

impl PartialEq for rama::net::socket::opts::Type

impl PartialEq for IpAddrRange

impl PartialEq for IpSubnets

impl PartialEq for IpNet

impl PartialEq for ServerVerifyMode

impl PartialEq for ApplicationProtocol

impl PartialEq for rama::net::tls::CertificateCompressionAlgorithm

impl PartialEq for rama::net::tls::CipherSuite

impl PartialEq for CompressionAlgorithm

impl PartialEq for DataEncoding

impl PartialEq for ECPointFormat

impl PartialEq for ExtensionId

impl PartialEq for rama::net::tls::ProtocolVersion

impl PartialEq for rama::net::tls::SignatureScheme

impl PartialEq for SupportedGroup

impl PartialEq for ClientVerifyMode

impl PartialEq for TransportProtocol

impl PartialEq for ProxyCredential

impl PartialEq for UserId

impl PartialEq for MemoryProxyDBInsertErrorKind

impl PartialEq for MemoryProxyDBQueryErrorKind

impl PartialEq for rama::proxy::haproxy::protocol::v1::Addresses

impl PartialEq for BinaryParseError

impl PartialEq for rama::proxy::haproxy::protocol::v1::ParseError

impl PartialEq for AddressFamily

impl PartialEq for rama::proxy::haproxy::protocol::v2::Addresses

impl PartialEq for rama::proxy::haproxy::protocol::v2::Command

impl PartialEq for rama::proxy::haproxy::protocol::v2::ParseError

impl PartialEq for rama::proxy::haproxy::protocol::v2::Protocol

Trait PartialEq

§How can I implement `PartialEq`?