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iOS Swift Functions and Optionals Functions Function Return Types

Posted by Gustav Gesar
Gustav Gesar
2,353 Points

Missing argument label XXX in call

I wrote a short line of code:

func area(a:Int,b:Int) -> Int{ return a * b }

print(area(10, 2))

Then, I get the error message:

"error: missing argument label 'b:' in call"

So, I must write the following for the code to compile:

print(area(10, b: 2)

But, when I write the following I get the error again:

ar(a: 10, b: 2)

"error: extraneous argument label 'a:' in call"

Why is this? Why can't I just write:

print(area(10, 2))

1 Answer

Brendan Whiting
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
Brendan Whiting
Front End Web Development Techdegree Graduate 84,735 Points
Brendan Whiting
.a{fill-rule:evenodd;}techdegree seal-36
Brendan Whiting
Front End Web Development Techdegree Graduate 84,735 Points

The first argument is an anonymous by default. The next arguments are not. So if you want them to be anonymous you add an underscore before it:

func area(a:Int, _ b:Int) -> Int{
    return a * b
}

And then you can call it without its label:

area(10, 2)

It seems arbitrary why they do this. But for a lot of functions the first (and maybe only) argument is usually self-explanatory, so if you had to use its label explicitly when calling it, it would be redundant. So this is just how they decided to set things up to make the largest number of programmers happy most of the time, but it's a trade off, and sometimes it just makes you override it and it's annoying.

Gustav Gesar
Gustav Gesar
2,353 Points

Thank you! Is it common to use external names? For example, I find it easies to call the function if I have names. For example:

func area(height a: Int, width b: Int) -> Int{ return a * b }

area(height: 10, width: 2)