Trait scrypto_test::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_test::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 AccountCollection

impl PartialEq for AccountFeature

impl PartialEq for AccountField

impl PartialEq for VersionedAccountAuthorizedDepositor

impl PartialEq for VersionedAccountDepositRule

impl PartialEq for VersionedAccountResourcePreference

impl PartialEq for VersionedAccountResourceVault

impl PartialEq for AccountError

impl PartialEq for radix_engine::blueprints::account::events::DepositEvent

impl PartialEq for RejectedDepositEvent

impl PartialEq for radix_engine::blueprints::account::events::WithdrawEvent

impl PartialEq for MetadataError

impl PartialEq for MetadataValidationError

impl PartialEq for MetadataCollection

impl PartialEq for MetadataFeature

impl PartialEq for MetadataField

impl PartialEq for VersionedMetadataEntry

impl PartialEq for RoleAssignmentError

impl PartialEq for RoleAssignmentCollection

impl PartialEq for RoleAssignmentFeature

impl PartialEq for RoleAssignmentField

impl PartialEq for VersionedRoleAssignmentAccessRule

impl PartialEq for VersionedRoleAssignmentOwner

impl PartialEq for ComponentRoyaltyCollection

impl PartialEq for ComponentRoyaltyFeature

impl PartialEq for ComponentRoyaltyField

impl PartialEq for VersionedComponentRoyaltyAccumulator

impl PartialEq for VersionedComponentRoyaltyMethodAmount

impl PartialEq for ComponentRoyaltyError

impl PartialEq for NodeInfo

impl PartialEq for SystemDatabaseCheckError

impl PartialEq for SystemNodeCheckError

impl PartialEq for SystemNodeType

impl PartialEq for SystemPartitionCheckError

impl PartialEq for IDAllocation

impl PartialEq for SystemReaderError

impl PartialEq for TypeCheckError

impl PartialEq for TypeInfoSubstate

impl PartialEq for StaleTreePart

impl PartialEq for TreeNodeV1

impl PartialEq for VersionedTreeNode

impl PartialEq for CreationStrategy

impl PartialEq for CostingError

impl PartialEq for FeeReserveError

impl PartialEq for RoyaltyRecipient

impl PartialEq for scrypto_test::prelude::costing::StorageType

impl PartialEq for AbortReason

impl PartialEq for AccessControllerCollection

impl PartialEq for AccessControllerError

impl PartialEq for AccessControllerFeature

impl PartialEq for AccessControllerField

impl PartialEq for AccessControllerPartitionOffset

impl PartialEq for AccessRule

impl PartialEq for AccessRuleNode

impl PartialEq for AccountPartitionOffset

impl PartialEq for Actor

impl PartialEq for ApplicationError

impl PartialEq for AuthError

impl PartialEq for AuthZoneError

impl PartialEq for AuthZoneField

impl PartialEq for BalanceChange

impl PartialEq for BatchPartitionStateUpdate

impl PartialEq for BlueprintHook

impl PartialEq for BlueprintPartitionType

impl PartialEq for BlueprintPayloadDef

impl PartialEq for BlueprintPayloadIdentifier

impl PartialEq for BlueprintType

impl PartialEq for BootLoaderField

impl PartialEq for BucketError

impl PartialEq for CallFrameDrainSubstatesError

§How can I implement `PartialEq`?