On Dec 12, 2012, at 6:36 AM, jonat...@mugginsoft.com wrote:
> On 12 Dec 2012, at 09:57, Andreas Grosam <agro...@onlinehome.de> wrote:
>> On 12.12.2012, at 10:19, Charles Srstka wrote:
>>> On Dec 12, 2012, at 3:03 AM, Andreas Grosam <agro...@onlinehome.de> wrote:
>>>
>>>> How can I check at runtime whether an object (id) is actually a block, and
>>>> not another kind of object?
>>>
>>> I don't think there's any good way of doing that right now. You could check
>>> the class of the block, but since the block classes are completely
>>> undocumented AFAIK, there's no guarantee that the class names won't change
>>> in some future release of OS X and break your code.
>> Thanks for the reply. I feared that.
>>
>> Currently, I resort to
>>
>>
>> if ([obj isKindOfClass: NSClassFromString(@"NSBlock")])
>> …
>>
>> which evaluates to YES if `obj` is a block. However, NSBlock is not a public
>> class, thus: NSClassFromString(@"NSBlock") which "works" as the time of
>> writing in Mac OS, and returns a class whose name is "NSBlock" (the real
>> block classes are named differently).
>>
>> I wish there was something official.
> You could perhaps make this a little less fragile.
>
> typedef void (^MyBlockType)(void);
>
> // we know this is a block
> void (^isaBlock)(void) = ^(void) {};
>
> MyBlockType aBlock = ^(void) {NSLog(@"I am a block");};
>
> id qua = aBlock;
>
> if ([qua isKindOfClass:[isaBlock class]]) {
> ((MyBlockType)qua)();
> }
This will not work for all cases. For example, a stack-based block versus one
that's been copied to the heap will have different classes, which are probably
siblings (i.e. [[_NSConcreteStackBlock class] isKindOfClass:[_NSMallocBlock
class]] == NO).
My solution to this issue has been the "exclusion" case, i.e. if (![obj
isKindOfClass:[anything my API contract says I can receive that isn't a
block]]) { /* it's a block by process of elimination */ }. Obviously this won't
work if your API contract says you can receive arbitrary objects.
-- Gwynne Raskind
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