Swift and params method default values

Question

In the A.swift file I have

class A {
    func c(d: String = "abc") {
        // (1)
    }
}

and in the B.swift file I have

class B {
   func z() {
      let aaa = A()
      aaa.c()
   }
}

extension A {
    func c(d: String = "abc", e: String = "123") {
        // (2)
    }
}

Now, I'd like to know: in z()is called (1) or (2)? And how is it decided?

Answer 1

Your class A has two functions, c(d:), and c(d:e:). In Swift, two functions can share the same “first name”, but be distinguished by their arguments. Hence, the “full name” of a function consists of its name and all of its parameter labels.

Replace the line

aaa.c()

with

aaa.c(d:e:)()

which calls the function c(d:e:) by its full name, and (2) will execute.

Note that aaa.c() is equivalent to aaa.c(d:)(). Swift appears to default to the function with the fewest parameters when the call is ambiguous; this may be the subject of a future Swift Evolution proposal, if it is not already.