Question

I am still learning Objective-C but I like to know the “why” behind everything I learn.

I would like to know why an Objective-C method requires that the types are enclosed in parentheses, such as:

- (IBAction) myAction: (UIButton *) sender;

Instead of:

- IBAction myAction: UIButton *sender;

I’ve tried finding answers and thought about it quite a bit but can’t seem to see what the reasoning is for.

What troubles me is sometimes I actually forget that the asterisk (*) needs to be inside the parentheses, sometimes I accidentally type the following incorrect signature:

- (IBAction) myAction: (UIButton) *sender;

As to me, this more logically represents the argument is a pointer, not the type.

Answer 1

That’s C casting syntax:

int foo = (int)bar;

Think of it as casting the parameters and return value to specific types.

In the very early days of Objective-C return values and parameters defaulted to the id type. So you’d see method declarations like this:

-myAction:sender;

For numerous reasons it became preferable to strongly type the return value and parameters in Objective-C code, to the point that all return values and parameters are strongly typed, even if they’re id:

- (IBAction)myAction:(id)sender;

The asterisk is also C syntax. UIButton* is a specific type, different from UIButton and UIButton**. You could do this:

typedef UIButton* UIButtonRef;

and then use UIButtonRef instead of UIButton*:

- (IBAction)myAction:(UIButtonRef)sender;