Question

I have seen a lot of code like this

header.h

@interface Foo : NSObject
{
  NSString *str;
}

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

and then in implementation

@implementation Foo
 @synthesize str = _str;
@end

I can’t understand what is the benefit of using such assignment ?

@synthesize str = _str;

Answer 1

It is just a common naming convention.

It is so that in your implementation, you can distinguish accessing a variable directly against accessing via the property accessor.

If you try and access str in your code, like [str length], the code won’t compile. You either need to do [self.str length] or [_str length].

… and as it’s an NSString immutable property, use copy, not retain.