[Cython] Type casts

[Stefan Behnel]

Hi Robert,

Robert Bradshaw wrote:
> Currently, in Cython, when x is a python object, <int>x gives the  
> address of x. This is counter-intuitive and rarely useful. (When it  
> is, one can always do <size_t><void *>x).
> 
> I would propose making <type>x do a conversion (the same as cdef type  
> y = x would) whenever type is a non-object type and x isn't, or vica- 
> versa. Between C types it already behaves this way, and between  
> Python objects it already has special meaning.

+1

The first thing I tried when I hit the bool expr problem, was changing

    if n is None or n == 0:

into

    if n is None or <bint>(n == 0):

which did not quite give the expected result.


> I would also propose something like
> 
> <ExtensionType?>x to be a cast into type ExtensionType *with* type  
> checking.

I think that's also a good idea.

BTW, we shouldn't forget to document syntax extensions in the wiki, so that
people (including Greg) know what works.

Stefan