On Sun, Jul 28, 2013 at 09:55:55AM +0000, Simon King wrote:
> When one uses ClasscallMetaclass for a class C and then defines a static
> method
> C.__classcall__, then creation of instances of C is done by this
> __classcall__.
> I just noticed that it is even possible that the resulting instances are
> not necessarily instances of C:
> ...
>
> Do we want such a behaviour? Or should ClasscallMetaclass.__call__ do
> some assertion that makes sure that it can only return instances of the
> class in question?
I don't have a strong use case, but just in case I'd rather decouple
syntax and semantic. Namely the __classcall__ hook is just about
implementing the syntax C(...). At the same time, I am happy setting
as recommendation that, in Sage, C(...) should return an instance of
C.
That's a bit like what happens for other special methods like __mul__:
the user usually expects a+b to be of the same type as a and b, but it
does not have to be so. Python provides this syntactic hook, but does
not enforce its semantic.
Cheers,
Nicolas
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
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