Question

Is it ok to use syntax like this:

Object.parent.property

or should I restrict it to one dot and one level only?

Answer 1

In general, it is okay to use:

a.b.c

However, if there are structures involved then it might not work. Consider the following class declaration:

@interface Circle : NSObject
@property (assign) NSPoint centre;
@end

In this case, the centre property is of type NSPoint, a structure (not a class!) that declares two members, x and y. Reading the x coordinate works:

CGFloat x = circle.centre.x;

and is equivalent to:

CGFloat x = [circle center].x;

but writing the x coordinate doesn’t:

circle.centre.x = 50;

because the left part of the assignment, called an lvalue, is not assignable. The assignment is trying to change a member variable of a return value, namely the structure returned by [circle centre].

You’ll have to to write this instead:

NSPoint centre = circle.centre;
centre.x = 50;
circle.centre = centre;