conversionaccess.hpp

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/*------------------------------------------------------------------------------
    Copyright Butterfly Energy Systems 2014-2015, 2022.
    Distributed under the Boost Software License, Version 1.0.
    http://www.boost.org/LICENSE_1_0.txt
------------------------------------------------------------------------------*/
 
#ifndef CPPWAMP_CONVERSION_ACCESS_HPP
#define CPPWAMP_CONVERSION_ACCESS_HPP
 
#include <sstream>
#include <string>
#include <utility>
#include "api.hpp"
#include "error.hpp"
#include "traits.hpp"
 
//------------------------------------------------------------------------------
//------------------------------------------------------------------------------
 
//------------------------------------------------------------------------------
/* Generates a metafunction that checks for the presence of a member.
   Adapted from
   http://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Member_Detector. */
//------------------------------------------------------------------------------
#define CPPWAMP_GENERATE_HAS_MEMBER(member)                             \
                                                                        \
template <typename T>                                                   \
class CPPWAMP_API HasMember_##member                                                \
{                                                                       \
private:                                                                \
    using Yes = char[2];                                                \
    using  No = char[1];                                                \
                                                                        \
    struct Fallback { int member; };                                    \
    struct Derived : T, Fallback { };                                   \
                                                                        \
    template <typename U> static No& test ( decltype(U::member)* );     \
    template <typename U> static Yes& test ( U* );                      \
                                                                        \
public:                                                                 \
    static constexpr bool result =                                      \
        sizeof(test<Derived>(nullptr)) == sizeof(Yes);                  \
};                                                                      \
                                                                        \
template < class T >                                                    \
struct has_member_##member                                              \
: public std::integral_constant<bool, HasMember_##member<T>::result>    \
{};
 
 
namespace wamp
{
 
//------------------------------------------------------------------------------
//------------------------------------------------------------------------------
class CPPWAMP_API ConversionAccess
{
public:
    template <typename TConverter, typename TObject>
    static void convert(TConverter& c, TObject& obj)
    {
        static_assert(
            has_member_convert<TObject>(),
            "The 'convert' function has not been specialized for this type. "
            "Either provide a 'convert' free function specialization, or "
            "a 'convert' member function.");
        obj.convert(c);
    }
 
    template <typename TConverter, typename TObject>
    static void convertFrom(TConverter& c, TObject& obj)
    {
        static_assert(has_member_convertFrom<TObject>(),
                      "The 'convertFrom' member function has not been provided "
                      "for this type.");
        obj.convertFrom(c);
    }
 
    template <typename TConverter, typename TObject>
    static void convertTo(TConverter& c, const TObject& obj)
    {
        static_assert(has_member_convertTo<TObject>(),
                      "The 'convertTo' member function has not been provided "
                      "for this type.");
        obj.convertTo(c);
    }
 
    template <typename TObject>
    static TObject defaultConstruct() {return TObject();}
 
    template <typename TObject>
    static TObject* defaultHeapConstruct() {return new TObject;}
 
private:
    CPPWAMP_GENERATE_HAS_MEMBER(convert)
    CPPWAMP_GENERATE_HAS_MEMBER(convertFrom)
    CPPWAMP_GENERATE_HAS_MEMBER(convertTo)
};
 
} // namespace wamp
 
#endif // CPPWAMP_CONVERSION_ACCESS_HPP