[Pyrex] Re: Re: Pyrex and C++

[David J. C. Beach]

On Wed, 2003-11-19 at 14:28, Mike Rovner wrote:
> Greg Ewing wrote:
> > Pyrex currently generates code which casts lvalues, e.g.
> >
> >    MyExtensionType *p;
> >    (PyObject *)p = some_pyobject_expr;
> >
> > which is apparently illegal in C++.
> 
> It seems to be legal C++. See ISO 5.4:
> """
>     The result of the expression (T) cast expression is of type T. The
> result is an lvalue if T is
>     a reference type, otherwise the result is an rvalue.
> """

It would seem to me that this means that the user would be required to
issue:

(PyObject*&) p = some_pyobject_expr;

(casting p to be a reference to a pointer.)

Pointer values are not "references" in the C++ sense of the word. 
Remember that C++ has an explicit "reference" type, denoted with an
ampersand (&).  This allows you to write functions that have IN/OUT
arguments without using pointers, for example:

void addOneTo(int& x) {
   ++x;
}

(or better yet...)

template<class T>
void increment(T& t) {
   ++t;
}

Not that either of these constitutes a particularly useful function...

Dave

-- 
David J. C. Beach
<beach at verinet.com>
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