Re: [boost] New dependency report

Subject: Re: [boost] New dependency report
From: Peter Dimov (lists_at_[hidden])
Date: 2014-06-07 11:46:19

John Maddock wrote:

> >> In fact in C++11 it makes sense to me have:
> >>
> >> namespace boost{ namespace mpl{
> >>
> >> template <bool b>
> >> using bool_ = std::integral_constant<bool, b>;

I have another solution, which appears good enough to go into Core. We could 
also enhance mpl::bool_ in the same way. Note that the trait knows nothing 
about bool_, but dispatch still works.

#include <boost/config.hpp>
#include <boost/core/enable_if.hpp>

//

template< bool V > struct bool_
{
    BOOST_STATIC_CONSTANT( bool, value = V );

    template< class T > bool_( T const &, typename boost::enable_if_c< 
T::value == V >::type * = 0 )
    {
    }
};

typedef bool_< false > false_;
typedef bool_< true > true_;

//

#include <boost/core/lightweight_test.hpp>

template< class T > struct is_pointer
{
    BOOST_STATIC_CONSTANT( bool, value = false );
};

template< class T > struct is_pointer< T* >
{
    BOOST_STATIC_CONSTANT( bool, value = true );
};

int f( true_ )
{
    return 5;
}

int f( false_ )
{
    return 11;
}

int main()
{
    BOOST_TEST( f( is_pointer< int* >() ) == 5 );
    BOOST_TEST( f( is_pointer< int >() ) == 11 );

    return boost::report_errors();
}