Mutating.swift

//: Playground - noun: a place where people can play

import Cocoa

var str = "Hello, playground"

struct Test {
    var value: Int = 0
    
    mutating func incrementer() -> () -> () {
        return {
            self.value += 1
            print(self)
        }
    }
}

var test = Test()
let increment = test.incrementer()

increment() // Test(value: 1)
increment() // Test(value: 2)
increment() // Test(value: 3)
increment() // Test(value: 4)

print(test) // Test(value: 0)