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

From: Pavel Kuznetsov (pavel_at_[hidden])
Date: 2004-08-24 09:48:56

David,

>> Here it is.

> Looks way too heavy to me for what it's accomplishing.
> How about:
> namespace error
> {
>   template <class T, class Value>
>   int
> dereferenceable_requires_lvalue_dereference(Value&);
> }
> 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>(
>              *static_cast<const T&>(*this)
>           ))
>      };
>      return &*static_cast<const T&>(*this);
>    }
> };
> ??
> 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);
    }
};

-- 
Pavel Kuznetsov
MetaCommunications Engineering
http://www.meta-comm.com/engineering