[MacRuby-devel] Understanding Pointer objects

[Laurent Sansonetti]

Hi Mark,

> Ah, that does work, and seems to have worked for a number of other things I am trying to do. 
> 
> The only problem now is when I have something like
> 
> 	value = Pointer.new '^v' # pointer to pointer to void
> 	AXUIElementCopyAttributeValue mail_object, 'AXHidden', value
> 
> In this case I am using it right now, it will be returning a boolean, but when I try to dereference it like
> 
> 	puts value[0][0] # => 120
> 
> it gives me a Fixnum, and then I can keep trying things like 
> 
> 	puts value[0][1] # => 104
> 	puts value[0][10000] # => 0
> 
> And I seem to get nowhere.
> 
> Is there a way to cast the data back into the type I want it to be? Or am I doing something dumb?

Looks like this function has the following declaration:

extern AXError  AXUIElementCopyAttributeValue (AXUIElementRef element, CFStringRef attribute, CFTypeRef *value);

So, the 3rd argument is is a CF object returned by reference.

You should be able to do the following then:

  ptr = Pointer.new(:id)
  AXUIElementCopyAttributeValue(mail_object, 'AXHidden', ptr)
  value = ptr[0]

To reply to your other question, it is possible to cast the type of a Pointer object, using the #cast! method. Sometimes this is useful when you get a void pointer from a native API and want to cast it into something more useful. But you should be careful, MacRuby will not prevent you from doing bad casts.

Laurent
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