Closures understanding

closures.swift

import UIKit

//Closures: Functions can be passed into another functions as parameters and can be returned from functions as well.

// Step 1
//func calculate (n1: Int, n2: Int) -> Int {
//    return n1 * n2
//}



func add (no1: Int, no2: Int) -> Int {
    return no1 + no2
}

func multiply (no1: Int, no2: Int) -> Int {
    return no1 * no2
}

//Step: 2
//now lets pass this func as parameter to calculate function step 1

//func calculate (n1: Int, n2: Int, operation: (Int, Int) -> Int) -> Int {
//    return n1 * n2
//}

//Now lets change the body of the Step 2 function to call the function that we passed

func calculate (n1: Int, n2: Int, operation: (Int, Int) -> Int) -> Int {
    return operation (n1, n2)
}

//Now pass operation func as param
//calculate(n1: 2, n2: 3, operation: add)
calculate(n1: 2, n2: 3, operation: multiply)


//Steps to convert func into closure with following example
func test (no1: Int, no2: Int) -> Int {
   return no1 + no2
}

// step a: remove func keyword, remove func name,
//(no1: Int, no2: Int) -> Int {
//   return no1 + no2
//}

// step b: move start bracket at start and replace it with in keyword
// {(no1: Int, no2: Int) -> Int in
//   return no1 + no2
//}

//Now lets replace closure in function call
// one must be thinking why we replaced in function call, well because we want this function to be called from within the calculate body

//calculate(n1: 2, n2: 3, operation:{(no1: Int, no2: Int) -> Int in
//   return no1 + no2
//})

//We can simplify it by removing datatype in func call params

//calculate(n1: 2, n2: 3, operation:{(no1, no2) -> Int in
//    return no1 + no2
//})

//We can simplify it further by removing the return type as compiler can infer the return type from return statement below

//calculate(n1: 2, n2: 3, operation:{(no1, no2) in
//    return no1 + no2
//})

// we can also remove return keyword as compiler can infer that closure is performing some func and it means return

//calculate(n1: 2, n2: 3, operation:{ (no1, no2) in no1 + no2 } )

// We can further simplify it because $0 means first param, $1 means second param

//let result = calculate(n1: 2, n2: 3, operation:{ $0 * $1 } )

//print(result)

//If last param is closure then we can omit its name and close the input section with closing bracket and remove the trailing bracket

let result = calculate(n1: 2, n2: 3) { $0 * $1 }
print(result)