[boost] Re: boost::dereferenceable<>::operator->() problem

From: David Abrahams (dave_at_[hidden])
Date: 2004-08-24 11:49:05

"Pavel Kuznetsov" <pavel_at_[hidden]> writes:

>> Does that work?
>
> Alas, that does not, since at least MSVC allows binding rvalue
> to non-const reference. But we can simplify original approach
> along these lines:
>
> namespace error
> {
>    template <class T, class Value>
>    int
>    dereferenceable_requires_lvalue_dereference(
>      Value& (T::*)()const);
> }
>
> template <class T, class P, class B =
>    ::boost::detail::empty_base>
> struct dereferenceable : B
> {
>     P operator->() const
>     {
>       enum
>       {
>         assertion = sizeof(
>           error::dereferenceable_requires_lvalue_dereference<T>(
>             &T::operator*
>           ))
>       };
>       return &*static_cast<const T&>(*this);
>     }
> };

No good, I'm afraid.  You can define a unary non-member operator*:

  struct X {};
  int operator*(X const&);

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com