On Feb 21, 2009, at 9:41 AM, Stuart Malin wrote:
So, I am curious as to why the default (retain) behavior of
@synthesize does just this?
What makes you think it does? There is no concrete promise about
how synthesized accessors are implemented, except that they
conform to the declared property attributes (retain vs. copy vs.
assign, etc.).
From "The Objective-C Programming Language" pdf (dated 2009-02-04)
page 59:
Setter Semantics
These attributes specify the semantics of a set accessor. They are
mutually exclusive.
assign
Specifies that the setter uses simple assignment. This is the
default.
retain
Specifies that retain should be invoked on the object upon
assignment. ( The default is assign.)
The previous value is sent a release message.
Note the last sentence from the above.
But as mmalc pointed out, the behavior is a function of atomicity.
Further from the quoted document (page 60):
If you do not specify nonatomic, then in a reference counted
environment a synthesized get accessor for
an object property uses a lock and retains and autoreleases the
returned value — the implementation will be
similar to the following:
[_internal lock]; // lock using an object-level lock
id result = [[value retain] autorelease];
[_internal unlock];
return result;
Because by default accessors are atomic, this seems to me to be
somewhat contrary to the earlier quote.
Ah, sorry to have said this. Further reading of the (updated) docs now
make it clear to me that these are harmonious.
You should trust that Apple is synthesizing just about the most
appropriate setter imaginable, given the declared property
attributes. Unless you need to do something else within the setter
-- that is, the setter has additional side effects -- just use
@synthesize.
Yes, Ken, I should :-)
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