Double pointer as Objective-C block parameter

Posted by George WS on Stack Overflow See other posts from Stack Overflow or by George WS
Published on 2013-10-21T21:20:29Z Indexed on 2013/10/21 21:53 UTC
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objective-c

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objective-c-blocks

Is it possible (and if so, safe) to create/use a block which takes a double pointer as an argument?

For instance:

- (void)methodWithBlock:(void (^)(NSError **error))block;

Additional context, research, and questions:

I'm using ARC.
When I declare the method above and attempt to call it, XCode autocompletes my method invocation as follows: [self methodWithBlock:^(NSError *__autoreleasing *error) {}]; What does __autoreleasing mean here and why is it being added? I presume it has something to do with ARC.
If this is possible and safe, can the pointer still be dereferenced in the block as it would be anywhere else?
In general, what are the important differences between doing what I'm describing, and simply passing a double pointer as a method parameter (e.g. - (void)methodWithDoublePointer:(NSError **)error;)? What special considerations, if any, should be taken into account (again assuming this is possible at all)?

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