ios - Function Parameter Names don't behave according to documentation -

according manual:

function parameter names

these parameter names used within body of function itself, , cannot used when calling function. these kinds of parameter names known local parameter names, because available use within function’s body.

    join("hello", "world", ", ")   func join(s1: string, s2: string, joiner: string) -> string {     return s1 + joiner + s2 } 

but code doesn't compile:

error: missing argument labels 's2:joiner:' in call join("hello", "world", ", ") ^ s2: joiner:

only when try 1 parameter, becomes optional

    join("hello")   func join(s1: string) -> string {     return s1 } 

even more annoying, it's not permissible use first 1 @ all:

    join(s1: "hello") 

extraneous argument label 's1:' in call join(s1: "hello")

did miss while reading documentation covering functions?

the behavior different between functions , methods.

for method, default behavior use local name external name arguments after first.

you can think of methods defaulting to:

func method(_ arg1: anyobject?, #arg2: anyobject?, #arg3: anyobject?) { } 

you can explicitly state how want handle arguments

func join(_ s1: string, _ s2: string, _ joiner: string) -> string {     return s1 + joiner + s2 } 

the swift programming language | language guide | methods

specifically, swift gives first parameter name in method local parameter name default, , gives second , subsequent parameter names both local , external parameter names default. convention matches typical naming , calling convention familiar writing objective-c methods, , makes expressive method calls without need qualify parameter names.