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Ok, I am confused! I used to use -> whenever I accessed my instance objects, but now I see that after I set them in my application:didFinishLaunching like this: 

self->counter = [NSNumber numberWithFloat:0.0f];

Down the road I got thrown out with an Exception, checked my debugger and saw that counter was pointing to a <non objective c object>

I changed the line to :

self.counter = [NSNumber numberWithFloat:0.0f];

And now I see in the debugger that I have yes another variable.

So, what is happening here?

Machavity
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Ted
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2 Answers2

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self->counter = [NSNumber numberWithFloat:0.0f]; uses direct access to an ivar. With self, it is equal to counter = [NSNumber numberWithFloat:0.0f]; where counter is an ivar. That is to say self-> is a redundant scope qualification within an instance method.

self.counter = [NSNumber numberWithFloat:0.0f]; is syntactic sugar for [self setCounter:[NSNumber numberWithFloat:0.0f]];. Specifically, the declaration dynamically messages the object's setter for counter. Although there are exceptions, you should favor using the accessor when not in a partially constructed/destructed state.

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justin
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    To add to this correct answer, the form `self->counter` is not only redundant in an instance method scope, it throws a warning (or error) outside that scope, unless the ivar is marked (bizarrely...) `@public` – FluffulousChimp Nov 20 '12 at 11:14
  • @NSBum Right +1, although access is inconsistent and complex in ObjC. If you are writing for newer ABIs, then access is checked correctly. Older ABIs or compilers, then may instead emit a warning. It's `@protected` by default if declared in an `@interface` and `@private` by default when declared in an `@implementation` block. clang also permits access to privates in an `@implementation` body (e.g. if using a static function) -- as expected, it is an error outside the `@implementation` body O_O – justin Nov 20 '12 at 11:23
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You're asking about the difference between iVars and properties. There's already a great answer on this question here.

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Rawkode
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