Re: [Boost-users] [Boost.Optional] Compilation error with boost::optional in Boost 1.49 and GCC 4.4.6

Subject: Re: [Boost-users] [Boost.Optional] Compilation error with boost::optional in Boost 1.49 and GCC 4.4.6
From: Jeffrey Lee Hellrung, Jr. (jeffrey.hellrung_at_[hidden])
Date: 2012-04-27 16:56:01

On Fri, Apr 27, 2012 at 12:47 PM, Jonathan Jones <
Jonathan.Jones_at_[hidden]> wrote:

> Hello,
>
> The following code fails to compile when using GCC 4.4.6 and
> boost::optional from Boost 1.49:
>

Hmmm...seems to build fine for me with MSVC9 (also Boost 1.49.0)

   #include <boost/optional/optional.hpp>
>    #include <boost/type_traits/is_convertible.hpp>
>
>    struct grill
>    {
>        template<typename U>
>        grill (U)
>        {}
>    };
>
>    template<typename T>
>    struct bar
>    {
>        template<typename U>
>        bar (U,
>             typename boost::is_convertible<U,T>::type* = 0)
>        {}
>    };
>
>    void foo()
>    {
>        typedef bar<grill> data_type;
>
>        boost::optional<data_type> opt;
>        boost::optional<data_type> opt2(opt); // this line
>        (void)opt2;
>    }
>
>
> Here are the error messages (I apologize for the long lines, I shortened
> them as much as possible by truncating the header paths):
>
>
> type_traits/is_convertible.hpp: In instantiation of ‘const bool
> boost::detail::is_convertible_basic_impl<boost::optional_detail::optional_base<bar<grill>
> >&, grill>::value’:
> type_traits/is_convertible.hpp:329:   instantiated from ‘const bool
> boost::detail::is_convertible_impl<boost::optional_detail::optional_base<bar<grill>
> >, grill>::value’
> type_traits/is_convertible.hpp:452:   instantiated from
> ‘boost::is_convertible<boost::optional_detail::optional_base<bar<grill> >,
> grill>’
> optional/optional.hpp:604:   instantiated from
> ‘boost::optional<T>::optional(const boost::optional<T>&) [with T =
> bar<grill>]’
> optional.cpp:25:   instantiated from here
> optional/optional.hpp:285: error:
> ‘boost::optional_detail::optional_base<T>::optional_base(const
> boost::optional_detail::optional_base<T>&) [with T = bar<grill>]’ is
> protected
> type_traits/is_convertible.hpp:170: error: within this context
> type_traits/is_convertible.hpp:170: error:   initializing argument 1 of
> ‘grill::grill(U) [with U = boost::optional_detail::optional_base<bar<grill>
> >]’
> optional/optional.hpp:308: error:
> ‘boost::optional_detail::optional_base<T>::~optional_base() [with T =
> bar<grill>]’ is protected
> type_traits/is_convertible.hpp:170: error: within this context
>
>
> This reproduction case is distilled from a real world example (not my
> code) where bar=boost::fusion::vector1 and grill=boost::function<void()>
>
> The code compiles fine using the same compiler and Boost 1.44.
>
> Any ideas on the root of the problem?
>

I can't figure it out from a quick glance through optional.hpp :( Can you
investigate what has changed in optional.hpp between 1.44 and 1.49?

- Jeff