Default arguments

Function parameters maybe given default values, in the following form:

func paintFace(color: String = "white") 
{ 
  print("I have painted my face \(color)") 
} 

It's probably clear already that the function can be called with color, or with none, in which case the default value is used:

paintFace() 
paintFace(color: "red") 

If we run the code above, we'll see the following output:

I have painted my face white
I have painted my face red

This can also be used with optional type parameters. This allows us to test for the presence of an argument to the function:

func paintWagon(color: String? = nil) 
{ 
  if let color = color { 
    print("I have painted the wagon \(color)") 
  } 
}