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iOS

Justin Cannon
Justin Cannon
3,465 Points

Objective C Pointer Question

Hi! Can someone please help me understand something about pointers in objective c?

I understand that we declare all objects with pointers. I understand why. What I don't understand is how we are able to call methods on what I would have guessed were memory addresses. For example,

NSNumber *foo = @45; [foo someMethod]

foo is a pointer to an NSNumber, right? Shouldn't foo just be a memory address? Why can I call a method on it? From everything I've been learning, I would have guessed this would be the syntax (using * to dereference and get the object value of the pointer):

[*foo someMethod]

Thanks!

2 Answers

Amit Bijlani
STAFF
Amit Bijlani
Treehouse Guest Teacher

There's a lot of magic going on behind the scenes. That method call you mentioned above is converted to a C function by the compiler which looks like: objc_msgsend(foo, @selector(someMethod)). If you want to go down that rabbit hole of understanding the Objective-C runtime then read: https://mikeash.com/pyblog/friday-qa-2012-11-16-lets-build-objc_msgsend.html

Matthew Reed
PLUS
Matthew Reed
Courses Plus Student 17,986 Points

The method is being called on the object that foo is pointed to. I'm guessing they made it that way so you don't have to type an asterisk every time you call a method.