Ditto/chaiscript/dispatchkit/boxed_cast.hpp

// This file is distributed under the BSD License.
// See "license.txt" for details.
// Copyright 2009-2012, Jonathan Turner ([email protected])
// Copyright 2009-2017, Jason Turner ([email protected])
// http://www.chaiscript.com

// This is an open source non-commercial project. Dear PVS-Studio, please check it.
// PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com


#ifndef CHAISCRIPT_BOXED_CAST_HPP_
#define CHAISCRIPT_BOXED_CAST_HPP_

#include "../chaiscript_defines.hpp"
#include "bad_boxed_cast.hpp"
#include "boxed_cast_helper.hpp"
#include "boxed_value.hpp"
#include "type_conversions.hpp"
#include "type_info.hpp"

namespace chaiscript {
class Type_Conversions;
namespace detail {
namespace exception {
class bad_any_cast;
}  // namespace exception
}  // namespace detail
}  // namespace chaiscript

namespace chaiscript 
{
 
  /// \brief Function for extracting a value stored in a Boxed_Value object
  /// \tparam Type The type to extract from the Boxed_Value
  /// \param[in] bv The Boxed_Value to extract a typed value from
  /// \returns Type equivalent to the requested type 
  /// \throws exception::bad_boxed_cast If the requested conversion is not possible
  /// 
  /// boxed_cast will attempt to make conversions between value, &, *, std::shared_ptr, std::reference_wrapper,
  /// and std::function (const and non-const) where possible. boxed_cast is used internally during function
  /// dispatch. This means that all of these conversions will be attempted automatically for you during
  /// ChaiScript function calls.
  ///
  /// \li non-const values can be extracted as const or non-const
  /// \li const values can be extracted only as const
  /// \li Boxed_Value constructed from pointer or std::reference_wrapper can be extracted as reference,
  ///     pointer or value types
  /// \li Boxed_Value constructed from std::shared_ptr or value types can be extracted as reference,
  ///     pointer, value, or std::shared_ptr types
  ///
  /// Conversions to std::function objects are attempted as well
  ///
  /// Example:
  /// \code
  /// // All of the following should succeed
  /// chaiscript::Boxed_Value bv(1);
  /// std::shared_ptr<int> spi = chaiscript::boxed_cast<std::shared_ptr<int> >(bv);
  /// int i = chaiscript::boxed_cast<int>(bv);
  /// int *ip = chaiscript::boxed_cast<int *>(bv);
  /// int &ir = chaiscript::boxed_cast<int &>(bv);
  /// std::shared_ptr<const int> cspi = chaiscript::boxed_cast<std::shared_ptr<const int> >(bv);
  /// const int ci = chaiscript::boxed_cast<const int>(bv);
  /// const int *cip = chaiscript::boxed_cast<const int *>(bv);
  /// const int &cir = chaiscript::boxed_cast<const int &>(bv);
  /// \endcode
  ///
  /// std::function conversion example
  /// \code
  /// chaiscript::ChaiScript chai;
  /// Boxed_Value bv = chai.eval("`+`"); // Get the functor for the + operator which is built in 
  /// std::function<int (int, int)> f = chaiscript::boxed_cast<std::function<int (int, int)> >(bv);
  /// int i = f(2,3);
  /// assert(i == 5);
  /// \endcode
  template<typename Type>
  decltype(auto) boxed_cast(const Boxed_Value &bv, const Type_Conversions_State *t_conversions = nullptr)
  {
    if (!t_conversions || bv.get_type_info().bare_equal(user_type<Type>()) || (t_conversions && !(*t_conversions)->convertable_type<Type>())) {
      try {
        return(detail::Cast_Helper<Type>::cast(bv, t_conversions));
      } catch (const chaiscript::detail::exception::bad_any_cast &) {
      }
    }


    if (t_conversions && (*t_conversions)->convertable_type<Type>())
    {
      try {
        // We will not catch any bad_boxed_dynamic_cast that is thrown, let the user get it
        // either way, we are not responsible if it doesn't work
        return(detail::Cast_Helper<Type>::cast((*t_conversions)->boxed_type_conversion<Type>(t_conversions->saves(), bv), t_conversions));
      } catch (...) {
        try {
          // try going the other way
          return(detail::Cast_Helper<Type>::cast((*t_conversions)->boxed_type_down_conversion<Type>(t_conversions->saves(), bv), t_conversions));
        } catch (const chaiscript::detail::exception::bad_any_cast &) {
          throw exception::bad_boxed_cast(bv.get_type_info(), typeid(Type));
        }
      }
    } else {
      // If it's not convertable, just throw the error, don't waste the time on the 
      // attempted dynamic_cast
      throw exception::bad_boxed_cast(bv.get_type_info(), typeid(Type));
    }

  }

}



#endif