Equatable

Built-in trait · Adopted with with Equatable

== compares two structs field by field, and two objects of a class by whether they are the same object. A type that adopts Equatable chooses its own rule instead.

class Money with Equatable {
    var cents: Int

    constructor(cents: Int) {
        self.cents = cents
    }

    @override
    func equals(other: Money): Bool {
        return self.cents == other.cents
    }
}

print(Money(500) == Money(500))   # prints true

Without Equatable, the two Money objects above would not be equal, since they are two different objects.

equals(other: Self): Bool

Whether this value and other count as equal. == runs it, and != is always its opposite.

Adopting is explicit. A type with an equals method that does not write with Equatable keeps the usual ==, and Emerald warns about it.

To use values with custom equality as dictionary keys or in a set, adopt Hashable as well.