Swift: difference between function calls

Question

I am new to Swift programming. I can not understand the following code. In the following code to call

• incrementBy method : I need to type numberOfTimes in the second argument. But,

• sampleFunc method : I do not need to enter lastName in the second argument.

  class Counter {
  var count: Int = 0
  func incrementBy(amount: Int, numberOfTimes : Int) {
      count += amount * numberOfTimes
  }
  }
  
  var counter = Counter()
  counter.incrementBy(1, numberOfTimes : 3)
  print(counter.count)
  
  func sampleFunc(firstName : String, lastName : String){
  print("Hello \(firstName) \(lastName)")
  }
  
  sampleFunc("Abel", "Rosnoski")
  

Why is there a subtle difference? Please explain.

Answer 1

( struct enum) , . , , . .

incrementBy(amount: Int, numberOfTimes : Int) , . , numberOfTimes, . :

counter.incrementBy(1, numberOfTimes : 3)

func sampleFunc(firstName : String, lastName : String) . . :

sampleFunc("Abel", "Rosnoski")

.

: User3441734 ( ) " . init , _". .

Answer 2

@NSNoob , , :

func sampleFunc(firstName : String, lastName : String) {}
sampleFunc("First", lastName: "Last")

:

func sampleFunc(firstName : String, _ lastName : String) {}
sampleFunc("First", "Last")

:

func sampleFunc(firstName firstName : String, lastName : String) {}
sampleFunc(firstName: "First", lastName: "Last")

:

func sampleFunc(firstName firstName : String, lastName : String = "Last") {}
sampleFunc(firstName: "First")

,

Answer 3

func a(param1:Double, param2:Double) -> Double {
    return param1*param2;
}

func a2(p1 param1:Double,p2 param2:Double) -> Double {
    return param1*param2;
}

As I understood and did some tests on the playground, you need to use parameter names if you do not define label labels.

var c = a(3.2,2.3)
c //gives error

var b = a(param1:3.2,param2:2.3);
b

var d = a2(p1:3.2,p2:2.3);
d

var e = a2(param1:3.2,param2:2.3)
e //gives error