Question

I have a problem understanding properties.
What kind of property should I write if I want an attribute not be modified by its accessors (return by copy) and be set by reference (retain).

Example :

MyType* theAttribute = MyObject.attribute;
[theAttribute changeSomething]; // Does not have to change the MyObject attribute, working with a copy return

MyType tmpObject = [[MyType alloc] init];
MyObject.attribute = tmpObject; // Want a retain here
[tmpObject release];

Answer 1

declare the property as retain in the header:

@property (nonatomic. retain) MyType *attribute;

In the implementation file synthesize the iVar:

@synthesize attribute;

But provide your own getter which will override the synthesized one:

- (MyType)attribute {
    return [attribute copy];
}

I know I’m not autoreleasing the returned object, but since the question doesn’t specify iOS, I’m writing this from the perspective of a garbage collected environment.