CODEWITHSUNDEEP
objective-cmemory-managementnsstringproperties
Aisha
Aisha

Reputation: 1559

What happens to a property if its value is overwritten?

Lets suppose I created a property tempStr that is of NSString type. I synthesized it obviously.

In one of my methods, I set the value of tempstr to be yellowcolor. Then just after that I reinitialized tempStr with redcolor.

So I wanna know what happens to the memory of tempStr in this case.

Thanx.

Upvotes: 1

Views: 150

Answers (2)

Marcin Świerczyński
Marcin Świerczyński

Reputation: 2312

It depends on what attribute you set for your property: retain, assign or copy.

  • @property (retain) NSString *tempStr: the old value (yellowcolor) would be released and the new value (redcolor) would be retained. The only exception is when yellowcolor == redcolor. Then nothing would happen, because old and new values are the same.
  • @property (assign) NSString *tempStr: there would be no release/retain operations. It is equal to changing just a pointer. So after this operations yellowcolor won't be released and you'll lost a reference to it (if there is no other reference to it in your code). So it can cause a memory leak.
  • @property (copy) NSString *tempStr: it's similar to retain but it call copy on new value instead of just retain, so it'd create a duplicate object in a memory. Considering NSString, it's equal to retain, because NSString is immutable, so there is no need to make a duplicate.

You can find some code examples here.

EDIT: As @Bavarious mentioned, copy is equal to retain only if you initialize this property with NSString. It won't be equal if you initialize it with NSMutableString, because this one is mutable, so the "proper" copy would be make.

Upvotes: 2

Wolfgang Schreurs
Wolfgang Schreurs

Reputation: 11834

A synthesized setter looks a bit like this:

- (void)setSomeString:(NSString *)newString
{
   if ([newString isEqualToString:someString]) return;

   [someString autorelease];
   someString = [newString copy]; // or [newString retain], depends how you defined the property ...
}

So the old value is released when the new value is assigned to the pointer.

Upvotes: 1

Related Questions