Antoine Pitrou, 23.08.2011 16:08:
On Tue, 23 Aug 2011 16:02:54 +0200
Stefan Behnel wrote:
"Martin v. Löwis", 23.08.2011 15:17:
Has this been considered before? Was there a reason to decide against it?
I think we simply didn't consider it. An early version of the PEP used
the lower bits for the pointer to encode the kind, in which case it even
stopped being a pointer. Modules are not expected to access this
pointer except through the macros, so it may not matter that much.
The difference is that you *could* access them directly in a safe way, if
it was a union.
So, for an efficient character loop, replicated for performance reasons or
for character range handling reasons or whatever, you could just check the
string kind and then jump to the loop implementation that handles that
type, without using any further macros.
Macros are useful to shield the abstraction from the implementation. If
you access the members directly, and the unicode object is represented
differently in some future version of Python (say e.g. with tagged
pointers), your code doesn't compile anymore.
Even with tagged pointers, you could just provide a macro that unpacks the
pointer to the buffer for a given string kind. I don't think there's much
more to be done to keep up the abstraction. I don't see a reason to prevent
users from accessing the memory buffer directly, especially not by
(accidental, as I understand it) obfuscation through a void*.
Stefan
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