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)

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.