Re: [boost] [type_traits][cw] is_convertible compile failure

From: Joaquín Mª López Muñoz (joaquin_at_[hidden])
Date: 2006-02-10 03:33:07

John Maddock ha escrito:

> >> ### mwcc Compiler:
> >> #      In: ..\..\..\boost\type_traits\is_convertible.hpp
> >> #    From: tricky_function_type_test.cpp
> >> # --------------------------------------
> >> #     158:         );
> >> #   Error:          ^
> >> #   function call '_m_check({lval} void (), int)' does not match
> >> #   'boost::detail::is_convertible_basic_impl<void (&)(),
> >> boost::detail::int_convertible>::_m_check(boost::detail::any_conversion,
> >> ...)' (static) #   'boost::detail::is_convertible_basic_impl<void
> >> (&)(),
> >> boost::detail::int_convertible>::_m_check(boost::detail::int_convertible,
> >> int)' (static) #    (point of instantiation: 'main()') #
> >> (instantiating: 'boost::is_enum<void ()>') #      (instantiating:
>
> I don't see any way around that unfortunately: the function call should be
> deduced to work OK: it does on EDG and gcc compilers, and ultimately all the
> possible implementations use either this method or the current one (or
> trivial variations).  Is there any other way to work around the original
> problem?

I'm afraid there ain't. This popped up from original code like

typename disable_if<is_convertible<const ChainedPtr,Type>,Type&>::type
operator()(const ChainedPtr& x)const;

which disables operator() when ChainedPtr satisfies the is_convertible
condition --basically I cannot do anything to prevent the problem as
ChainedPtr is a user-provided type.

Excuse my beating this problem to death, but maybe there's still
some hope: If I'm getting it right, Stefan's tests show that CW works with
the EDG pp-branch technique EXCEPT when From is a function
type. Cannot we do then the following?

1. If is_function<From>::value, use the current  tecnhique.
2. Else, use the EDG tecnhique.

The attached file implements this idea. I cannot test it myself under CW,
it'd be great is someone can give it a try.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo