protocol Comparable Instances of conforming types can be compared using relational operators, which define a strict total order. A type conforming to Comparable need only supply the < and == operators; default implementations of <=, >, >=, and != are supplied by the standard library: struct Singular : Comparable {} func ==(x: Singular, y: Singular) -> Bool { return true } func <(x: Singular, y: Singular) -> Bool { return false } Axioms, in addition to those of Equatable: x == y implies x <= y, x >= y, !(x < y), and !(x > y) x < y implies x <= y and y > x x > y implies x >= y and y < x x <= y implies y >= x x >= y implies y <= x Inheritance Equatable View Protocol Hierarchy → Import import Swift Instance Methods func <(_:rhs:) Required A strict total order over instances of Self. Declaration func <(lhs: Self, rhs: Self) -> Bool func <=(_:rhs:) Declaration func <=(lhs: Self, rhs: Self) -> Bool func ==(_:rhs:) Required Return true if lhs is equal to rhs. Equality implies substitutability. When x == y, x and y are interchangeable in any code that only depends on their values. Class instance identity as distinguished by triple-equals === is notably not part of an instance's value. Exposing other non-value aspects of Equatable types is discouraged, and any that are exposed should be explicitly pointed out in documentation. Equality is an equivalence relation x == x is true x == y implies y == x x == y and y == z implies x == z Inequality is the inverse of equality, i.e. !(x == y) iff x != y. Declaration func ==(lhs: Self, rhs: Self) -> Bool Declared In Equatable func >(_:rhs:) Declaration func >(lhs: Self, rhs: Self) -> Bool func >=(_:rhs:) Declaration func >=(lhs: Self, rhs: Self) -> Bool