Question

Here is my code
Class.h

@interface Class : NSObject
{
  NSString *str;
}

@property (nonatomic, copy) NSString *str;
@end

@implementation Class
@synthesize str = _str;

-(void)someMethod
{
  self.str = @"This is a string";
}

Here I can’t figure out does self.str access str ivar directly or by getter and setter methods “generated” by synthesize directive ?

Answer 1

If you use self.str = … it’s just syntatactic sugar around [self setStr:…]. So you are going through the setter method. Even if you get a value with self.str you are going through an accessor – which is useful to know if you are implementing lazily loaded properties.

you can only access the iVar directly in your case with _str because you’ve (correctly, In My Opinion) declared that to be the name of the backing store.

Edited to add

There is a problem with your example – you’ve defined the iVar str which isn’t being used (the iOS uses a modern runtime where you don’t need to declare iVars for properties that you synthesize). So although your code is writing to a backing store _str and that is the store that is being used through self.str if you were to access the str variable directly you would be using the declared iVar, not the one that you have a property for.