Swift closure : Capturing value, Escaping Closures

//1. Closure : Capturing value


func makeIncrement( forIncrement amount: Int) -> ()->Int {
    var sum = 0 // this is captured value
    func add () -> Int {
        sum += amount
        return sum
    }
    return add
}

let incrementBy5 = makeIncrement(forIncrement:5)
print(incrementBy5())
print(incrementBy5())
let incrementBy3 = makeIncrement(forIncrement:3)
print(incrementBy3())
print(incrementBy3())


//Closures are Reference Type
let incrementTemp = incrementBy3
print(incrementTemp())


//2. Closure : Escaping Closures
/*
A closure is said to escape a function when the closure is passed as an argument to the function, but is called after the function returns.
*/

var completionHandlers: [() -> Void] = []
func someFunctionWithEscapingClosure(completionHandler: @escaping  () -> Void) {
    completionHandlers.append(completionHandler)    
    // closure is not called in this scope. @escaping required
    // completionHandler() // closure is called in this scope. @escaping not required
}

func someFunctionWithNonescapingClosure(closure: () -> Void) {
    closure()
}

class SomeClass {
    var x = 10
    func doSomething() {
        someFunctionWithEscapingClosure { self.x = 100 }
        someFunctionWithNonescapingClosure { x = 200 }
    }
}

let instance = SomeClass()
instance.doSomething()
print(instance.x)
// Prints "200"
completionHandlers.first?()
print(instance.x)
// Prints "100”