How do I implement Swift's Comparable protocol?

Question

How do I use the Comparable protocol in Swift? In the declaration it says I'd have to implement the three operations <, <= and >=. I put all those in the class but it doesn't work. Also do I need to have all three of them? Because it should be possible to deduce all of them from a single one.

Answer 1

The Comparable protocol extends the Equatable protocol -> implement both of them

In Apple's Reference is an example from Apple (within the Comparable protocol reference) you can see how you should do it: Don't put the operation implementations within the class, but rather on the outside/global scope. Also you only have to implement the < operator from Comparable protocol and == from Equatable protocol.

Correct example:

class Person : Comparable {     let name : String      init(name : String) {         self.name = name     } }  func < (lhs: Person, rhs: Person) -> Bool {     return lhs.name < rhs.name }  func == (lhs: Person, rhs: Person) -> Bool {     return lhs.name == rhs.name }  let paul = Person(name: "Paul") let otherPaul = Person(name: "Paul") let ben = Person(name: "Ben")  paul > otherPaul  // false paul <= ben       // false paul == otherPaul // true