Swift Tutorial - Tutorialspoint

Mutating Instance Methods

Instance methods can also be mutated when declared as extensions.

Structure and enumeration methods that modify self or its properties must mark the
instance method as mutating, just like mutating methods from an original implementation.

extension Double {

mutating func square() {

let pi = 3.1415

self = pi * self * self

}

}

var Trial1 = 3.3

Trial1.square()

println("Area of circle is: \(Trial1)")

var Trial2 = 5.8

Trial2.square()

println("Area of circle is: \(Trial2)")

var Trial3 = 120.3

Trial3.square()

println("Area of circle is: \(Trial3)")

When we run the above program using playground, we get the following result:

Area of circle is: 34.210935

Area of circle is: 105.68006

Area of circle is: 45464.070735

Subscripts

Adding new subscripts to already declared instances can also be possible with extensions.

extension Int {

subscript(var multtable: Int) - > Int {