I swear, this will be the most simple way to write a closure.

Lets consider the return type to be Void

Start with the input parameters

()

Next lets move on to the return type

()

Now lets combine the above statements

() -> ()

Let’s make use of this, as a completion handler

	func testCompletionHandlers(completion: (Int)->()) -> Void {
		completion(5)
	}

        testCompletionHandlers { number in
		print("number")
	}

It’s that simple.

Now, lets use this logic when using a Map

let collection = input.map { (elementOfCollection) -> ResultType in
       return
}

To make it easier, the closure is very similar to the one we described above.

let users = [Info(firstName: "tom", lastName: "jones"), Info(firstName: "tdddom", lastName: "jak"), Info(firstName: "atom", lastName: "jones"), Info(firstName: "taom", lastName: "jones")]
            let siblings = users.map { users in
	    return users.lastName
	}
print("siblings \(siblings)")

You can use this logic to construct your completion handlers