Question

Assume that I have this piece of code:

@interface Foo : NSObject {
    Bar *bar;
}

@property (retain, nonatomic) Bar *bar;

@end

When using this field/property, is there any difference between lines:

[self.bar doStuff];

and

[bar doStuff];

?

When doing assignment, property method will perform correct retaining, but what about the read access to the property, as described above? Is there any difference?

Answer 1

There is a big difference.
[self.bar doStuff] is equivalent to [[self bar] doStuff]

[bar doStuff] is equivalent to [self->bar doStuff]

The former uses the accessor method, the latter just accesses the instance variable bar directly.

If you use the @synthesize directive on your bar property, the compiler will generate two methods for you:

- (void)setBar:(Bar*)b;
- (Bar*)bar;

Also note, that the compiler generated setter method is retaining your Bar instance as you told it in the @property declaration.