On Oct 17, 2008, at 1:25 PM, Ignacio Enriquez wrote:
Second: Let me see If I understood. they should be copy since all the
classes all conform to NSCopying. this means that all (and I mean ALL
) properties should be "copy"?? (since all objects inherits from
NSObject and this class conform to NSCopying!?) I Think I missing
something here.
What gives you the impression that NSObject (and thus all of its
subclasses) conform to NSCopying?
A property should be copy when you are interested in the *value* of
the thing being set.
A property should be retain when you are interested in maintaining a
relationship to the thing being set.
Consider a Person object.
Person *person1 = [[Person alloc] init];
Person *person2 = [[Person alloc] init];
NSMutableString *string = [NSMutableString string];
[string setString: @"Jim"];
person1.name = string;
[string setString: @"Ignacio"];
person2.name = string;
If name were specified as
@property(retain) NSString *name;
then both people would now be named "Ignacio" (person1 having been
changed by side effect), which is not what we want in this situation.
However, if we had a parent property, we are interested in the
relationship to the parent (i.e. we don't want a separate copy), so
retain, not copy, would be more appropriate here.
Jim
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