Re: Old Meyers C++ compiler test no longer valid?

From:

Bart van Ingen Schenau <bart@ingen.ddns.info>

Newsgroups:

comp.lang.c++.moderated

Date:

Fri, 17 Jul 2009 15:27:28 CST

Message-ID:

<2677599.VmPV1yjcLH@ingen.ddns.info>

Russ Bryan wrote:

I dug up this compiler test submitted to Digital Mars by Scott Meyers
in 2001. At the time, the claim was that Borland and Comeau were able
to compile this code successfully. I've just tried this code with the
Comeau test compiler and VS2008 SP1 and both of them report errors on
lines 32 and 34.

const class {
public:
   template <class T>
   operator T*() const {return 0;}

   template <class C, class T>
   operator T C::*() const {return 0;}

For some reason, the deduction of C and/or T fails if the conversion is
to a const-qualified member function.
Adding the overload
template <class C, class T>
operator T const C::*() const {return 0;}

clears the error, but I am unable to figure out why that extra overload
should be needed.

} null = {};

class A {
public:
   int f (char, int);
   int f (char, double);
   void f (const char *) const;
};

class B {};

int main() {
   int (A::*pmf)(char, int) = &A::f;
   pmf = null;
   int (A::*pmf2)(char, double) = &A::f;
   pmf2 = null;
   void (A::*pmf3)(const char*) const = &A::f;
   pmf3 = null; <<< No user-defined operator can perform this
conversion

   void (B::*pmf4)() const = null; <<< No user-defined operator can
perform this conversion
}

I was wondering if anyone has some insight about this. Are these
calls actually illegal due to some clarification in the standard, or
has compiler conformance on Comeau regressed?

Bart v Ingen Schenau
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