[Usage of Closures]

closure-usage.swift

let guests = ["Ahmad", "Mohsen", "Ehsan"]

// map closure
guests.map {
	print("Hello \($0)")
}
let messages = guests.map { (name) -> String in
	return name + "!"
}
print(messages)

// reusable closures
let greeting = {
	(name: String) -> Void in
	print("Hello guest named \(name)")
}
let sayGoodbye : (String) -> () = {
	print("Goodbye \($0)")
}
guests.map(greeting)
guests.map(sayGoodbye)

let greeting2 = {
	(name: String) -> Void in
	if(name.hasPrefix("A")) {
		print("Hello guest named \(name)")
	} else {
		print("Dear \(name), you are not invited")
	}
}
guests.map(greeting2)

// preservation of variables inside closures
func temperatures(calculate:(Int)->Void) {
	let numbers = [72,74,76,68,70,72,66]
	numbers.map(calculate)
}
func testFunction() {
	var total = 0
	var count = 0
	let addTemps = {
		(num: Int) -> Void in
		total += num
		count += 1
	}
	temperatures(calculate: addTemps)
	print("Total: \(total)")
	print("Count: \(count)")
	print("Average: \(total/count)")
}
testFunction()

// usage 2
struct TestType {
	typealias getNumClosure = ((Int, Int) -> Int)
	
	var numOne = 5
	var numTwo = 8
	
	var results = 0;
	
	mutating func getNum(handler: getNumClosure) -> Int {
		results = handler(numOne,numTwo)
		print("Number to Use:  \(results)")
		return results
	}
}
var max: TestType.getNumClosure = {
	if $0 > $1 {
		return $0
	} else {
		return $1
	}
}
var min: TestType.getNumClosure = {
	if $0 < $1 {
		return $0
	} else {
		return $1
	}
}
var multiply: TestType.getNumClosure = {
	return $0 * $1
}
var second: TestType.getNumClosure = {
	return $1
}
var answer: TestType.getNumClosure = {
	_ = $0 + $1 // to prevent error of not using parameters
	return 42
}
var myClass = TestType()
myClass.getNum(handler: max)
myClass.getNum(handler: min)
myClass.getNum(handler: multiply)
myClass.getNum(handler: second)
myClass.getNum(handler: answer)