On 2010.08.18, at 2:08 PM, Sherm Pendley wrote:
Indeed, on that very page, at
<http://developer.apple.com/mac/library/documentation/cocoa/conceptual/MemoryMgmt/Articles/mmAccessorMethods.html#//apple_ref/doc/uid/TP40003539-SW6
>,
it gives this example:
- (NSString*) title {
return [[title retain] autorelease];
}
...
"Because the object returned from the get accessor is autoreleased
in the current scope, it remains valid if the property value is
changed.
This makes the accessor more robust, but at the cost of additional
overhead."
Yes, but on the same page, see "Technique 3" where autorelease is not
used at all. The docs comment:
Its [Technique 3] disadvantage is that the old value may be
deallocated immediately (if there are no other owners), which will
cause a problem if another object is maintaining a non-owning
reference to it.
In your example the caller has such a non-owning reference.
Implementing -stringByReplacing... as "return [[self retain]
autorelease];" makes the same guarantee, that the object returned by
-stringByReplacing... will remain valid if the original string is
released.
Yes, but there's no guarantee which technique -stringByReplacing..
will use internally. Methods are free to use whatever implementation
they feel is most appropriate. Thus one must be prepared for the
original string to be returned directly, with no additional autorelease.
~Martin
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