On Thu, Jan 24, 2013 at 12:08:15PM -0800, Nils Bruin wrote:
> Ouch, yes that is a fundamental problem. What one should have is a
> custom `__new__` on UniqueRepresentation, with the python semantics,
> not the cython __cinit__ (formerly called and still accepted __new__).
> And there you can see the problem for how to arrange that properly in
> inheritance (let alone multiple inheritance!). In cython, the actual
> memory allocation happens on subclass level because it knows the full
> memory layout. superclasses only get to initialize that memory.
> However, the whole point of UniqueRepresentation is to avoid new
> allocation under select circumstances and return an old instance. In
> cython, a superclass fundamentally can't do that.
>
> Instead, one would have to mandate creation via a factory function
> which can do the lookup (I guess metaclasses are just a way to
> formalize factory functions and incorporate them into inheritance). In
> the current cython programming model ensuring uniqueness cannot be
> done upon instantiation, because your earliest hook is `__cinit__`
> when the new instance already is allocated.
Shall we ask the Cython devs to implement the __classcall__ protocol?
Then we could merge the factory function and the class in Cython
classes as is done by UniqueRepresentation.
Cheers,
Nicolas
--
Nicolas M. Thiéry "Isil" <[email protected]>
http://Nicolas.Thiery.name/
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