On Apr 2, 2009, at 13:54 , Michael Ash wrote:
On Thu, Apr 2, 2009 at 3:20 PM, Marcel Weiher
<marcel.wei...@gmail.com> wrote:
On Apr 1, 2009, at 21:44 , Michael Ash wrote:
On Thu, Apr 2, 2009 at 12:33 AM, Ryan Joseph
[distinguishing between NSArray and CFArray]
The test cannot be performed, because the question does not make any
sense.
While this answer is mostly true for what the original poster is
trying to
accomplish (as far as I can tell), it is actually not true.
An NSCFArray and a CFArray are indistinguishable as described, and
if you as
for an NSArray, you will typically get an NSCFArray.
However, an actual NSArray that is not an NSCFArray will be
different and
distinguishable. This distinction is also not just academic, but
quite
important because it is used by CoreFoundation to know wether to
call its
own functions or send a message to the object in question, allowing
custom
NSArray subclasses to be used in CFArray calls.
No, you're examining an entirely different question, which is whether
a particular object is the built-in provided NSArray subclass or a
custom subclass.
No. I am examining the question wether a CFArray can be distinguished
from an NSArray:
On Apr 1, 2009, at 21:44 , Michael Ash wrote:
I'm trying to determine at runtime if a type is CoreFoundation or
Cocoa, for
example NSArray/CFArray. [...]
The test cannot be performed, because the question does not make any
sense.
Your answer is correct if and only if the NSArray in question is a
NSCFArray. If the NSArray in question is not a NSCFArray, the
question is valid (thought possibly not what the original author
intended) and the test can be easily performed.
Of course you can tell those apart, just like you can
distinguish between an NSTextField and an NSButton. But they're *both*
NSViews, and any NSArray subclass is still an NSArray. And any NSArray
is also a CFArray.
This turns out not to be the case.
1. C
If you look at it from the C perspective, a CFArray is a very specific
structure that has no relationship to your NSArray subclass. So in
CF, the statement is clearly false. However, the CFArray functions
have special-case code to handle different types of objects
transparently. However, for me that "if" statement clearly shows that
they are *different* rather than the same, otherwise you wouldn't need
the if statement.
2. Objective-C
From the Objective-C perspective, the equivalence is NSCFArray =
CFArray. However, my custom NSArray subclass inherits from NSArray,
not NSCFArray. It does not have any relationship with NSCFArray
except a common ancestor:
NSArray
/ \
NSCFArray MYNSArray
Allowing your logic, just about any two classes would actually be
equivalent, because virtually all of them have NSObject as a common
ancestor.
It may have a different implementation from the
normal CFArray, but there's nothing weird about that: welcome to
object oriented programming.
The compatibility that you see and that is confusing you is not due to
the fact that there is an isa relationship, but due to non-isa
compatibility and lots of hard-coded work.
Cheers,
Marcel
_______________________________________________
Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)
Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com
Help/Unsubscribe/Update your Subscription:
http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com
This email sent to arch...@mail-archive.com
