Swift Tutorial - Swift Extensions

We can use extensions to add methods and computed properties to an existing class, structure, or enumeration.

Example

The following code shows how to extend the Person Class

class Person {
    var age:Int = 0
}

extension Person {
    var yearsToRetire:Int {
        get{
            return 65 - self.age
        }
    }
}

var p = Person()
p.age = 40

println(p.yearsToRetire)