Protocols and Extensions swift -

i new swift , learning swift "the swift programming language(swift 3 beta)". below simple example book of protocol extension

protocol exampleprotocol {      var simpledescription: string {get}      mutating func adjust() }  class simpleclass: exampleprotocol {      var simpledescription: string = "a vert simple class."      var anotherproperty: int = 69105      func adjust() {          simpledescription += "now 100% adjusted."     }  }  var = simpleclass()  a.adjust()  let adescripition = a.simpledescription  struct simplestructure: exampleprotocol {      var simpledescription: string = "a simple structure"      mutating func adjust() {          simpledescription += "(adjusted)"     }  }  var b = simplestructure()  b.adjust()  let bdescription = b.simpledescription  extension int: exampleprotocol{      var simpledescription : string {          return "the number \(self)"     }      mutating func adjust() {          self += 42     } }  //var c = simpleclass() //c.adjust() print(7.simpledescription) 

the end print result "the number 7\n". can see in extension, have mutating function add 42 self. question how can call mutating function in extension result added value of +42.

how call mutating function in extension result added value of +42.?

the function results in added value of +42 adjust() function of int. call it, run this:

var c = 7 c.adjust() print(c) 

c 49 (7 + 42)