Trait scrypto::prelude::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):

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.

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.

§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);

Required Methods§

source

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

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

Provided Methods§

source

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

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

Trait scrypto::prelude::PartialEq

§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 AddressBech32DecodeError

impl PartialEq for AddressBech32EncodeError

impl PartialEq for AttachedModuleId

impl PartialEq for KeyValueStoreDataSchema

impl PartialEq for ModuleId

impl PartialEq for FallToOwner

impl PartialEq for MetadataConversionError

impl PartialEq for Proposer

impl PartialEq for Role

impl PartialEq for DefaultDepositRule

impl PartialEq for ResourcePreference

impl PartialEq for TimePrecisionV1

impl PartialEq for TimePrecisionV2

impl PartialEq for BlueprintPartitionType

impl PartialEq for BlueprintPayloadDef

impl PartialEq for BlueprintPayloadIdentifier

impl PartialEq for BlueprintType

impl PartialEq for FunctionAuth

impl PartialEq for InputOrOutput

impl PartialEq for KeyOrValue

impl PartialEq for MethodAuthTemplate

impl PartialEq for PartitionDescription

impl PartialEq for RoleSpecification

impl PartialEq for SystemInstruction

impl PartialEq for VmType

impl PartialEq for AccessRule

impl PartialEq for AccessRuleNode

impl PartialEq for GlobalCaller

impl PartialEq for MethodAccessibility

impl PartialEq for NonFungibleDataSchema

impl PartialEq for OwnerRole

impl PartialEq for OwnerRoleUpdater

impl PartialEq for ParseNonFungibleGlobalIdError

impl PartialEq for ProofRule

impl PartialEq for ResourceError

impl PartialEq for ResourceFeature

impl PartialEq for ResourceOrNonFungible

impl PartialEq for ResourceType

impl PartialEq for WithdrawStrategy

impl PartialEq for InstructionOutput

impl PartialEq for ComponentCastError

impl PartialEq for ObjectStubHandle

impl PartialEq for ParseBlsPublicKeyError

impl PartialEq for ParseBlsSignatureError

impl PartialEq for ParseEd25519PublicKeyError

impl PartialEq for ParseEd25519SignatureError

impl PartialEq for ParseHashError

impl PartialEq for ParseSecp256k1PublicKeyError

impl PartialEq for ParseSecp256k1SignatureError

impl PartialEq for scrypto::crypto::PublicKey

impl PartialEq for PublicKeyHash

impl PartialEq for ManifestCustomExtension

impl PartialEq for ManifestCustomTraversal

impl PartialEq for ManifestCustomValue

impl PartialEq for ManifestCustomValueKind

impl PartialEq for ManifestToRustValueError

impl PartialEq for RustToManifestValueError

impl PartialEq for ManifestAddress

impl PartialEq for ManifestExpression

impl PartialEq for ManifestNonFungibleLocalId

impl PartialEq for ManifestNonFungibleLocalIdValidationError

impl PartialEq for ParseManifestAddressReservationError

impl PartialEq for ParseManifestBlobRefError

impl PartialEq for ParseManifestBucketError

impl PartialEq for ParseManifestDecimalError

impl PartialEq for ParseManifestExpressionError

impl PartialEq for ParseManifestPreciseDecimalError

impl PartialEq for ParseManifestProofError

impl PartialEq for OwnValidation

impl PartialEq for ReferenceValidation

§How can I implement `PartialEq`?