> No, you misunderstand. There is (in the scheme I'm vaguely recalling)
> _nothing_ inside the instances
> which holds or points to something which holds the retain count.
>
> There is another data structure entirely which maps from object addresses to
> a retain count.
Yes I see, that's also what Jean-Daniel is saying. In which case, my bytewise
copy scheme should work, since if a and b are (or derive from) NSObject then if
I do this:
*b = *a;
the retain count of (b) will be unaffected (which is what you want) and remains
independent of (a) since retain counts are tied to object addresses, not
content. The code I posted before should therefore produce the following
results (prediction, untested, fingers crossed):
NSObject *a = [[NSObject alloc] init];
printf ("%d\n", [a retainCount]); // 1
NSObject *b = [[[NSObject alloc] init] retain];
printf ("%d\n", [b retainCount]); // 2
*b = *a;
printf ("%d\n", [b retainCount]); // 2
[b retain];
printf ("%d\n", [b retainCount]); // 3
printf ("%d\n", [a retainCount]); // 1
I reckon my scheme might actually be faster Ben, if you benchmark it. Without
the assert it's just a method call and a memcpy, which the compiler knows the
size of and can therefore optimise. Only you can decide whether either
approach is worth the risk.
Paul 'quick and dirty' Sanders.
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