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Editing: nested_exception.h

// Nested Exception support header (nested_exception class) for -*- C++ -*-

// Copyright (C) 2009-2018 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file bits/nested_exception.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{exception}
 */

#ifndef _GLIBCXX_NESTED_EXCEPTION_H
#define _GLIBCXX_NESTED_EXCEPTION_H 1

#pragma GCC visibility push(default)

#if __cplusplus < 201103L
# include <bits/c++0x_warning.h>
#else

#include <bits/c++config.h>
#include <bits/move.h>

extern "C++" {

namespace std
{
  /**
   * @addtogroup exceptions
   * @{
   */

/// Exception class with exception_ptr data member.
  class nested_exception
  {
    exception_ptr _M_ptr;

public:
    nested_exception() noexcept : _M_ptr(current_exception()) { }

nested_exception(const nested_exception&) noexcept = default;

nested_exception& operator=(const nested_exception&) noexcept = default;

virtual ~nested_exception() noexcept;

[[noreturn]]
    void
    rethrow_nested() const
    {
      if (_M_ptr)
	rethrow_exception(_M_ptr);
      std::terminate();
    }

exception_ptr
    nested_ptr() const noexcept
    { return _M_ptr; }
  };

template<typename _Except>
    struct _Nested_exception : public _Except, public nested_exception
    {
      explicit _Nested_exception(const _Except& __ex)
      : _Except(__ex)
      { }

explicit _Nested_exception(_Except&& __ex)
      : _Except(static_cast<_Except&&>(__ex))
      { }
    };

// [except.nested]/8
  // Throw an exception of unspecified type that is publicly derived from
  // both remove_reference_t<_Tp> and nested_exception.
  template<typename _Tp>
    [[noreturn]]
    inline void
    __throw_with_nested_impl(_Tp&& __t, true_type)
    {
      using _Up = typename remove_reference<_Tp>::type;
      throw _Nested_exception<_Up>{std::forward<_Tp>(__t)};
    }

template<typename _Tp>
    [[noreturn]]
    inline void
    __throw_with_nested_impl(_Tp&& __t, false_type)
    { throw std::forward<_Tp>(__t); }

/// If @p __t is derived from nested_exception, throws @p __t.
  /// Else, throws an implementation-defined object derived from both.
  template<typename _Tp>
    [[noreturn]]
    inline void
    throw_with_nested(_Tp&& __t)
    {
      using _Up = typename decay<_Tp>::type;
      using _CopyConstructible
	= __and_<is_copy_constructible<_Up>, is_move_constructible<_Up>>;
      static_assert(_CopyConstructible::value,
	  "throw_with_nested argument must be CopyConstructible");
      using __nest = __and_<is_class<_Up>, __bool_constant<!__is_final(_Up)>,
			    __not_<is_base_of<nested_exception, _Up>>>;
      std::__throw_with_nested_impl(std::forward<_Tp>(__t), __nest{});
    }

// Determine if dynamic_cast<const nested_exception&> would be well-formed.
  template<typename _Tp>
    using __rethrow_if_nested_cond = typename enable_if<
      __and_<is_polymorphic<_Tp>,
	     __or_<__not_<is_base_of<nested_exception, _Tp>>,
		   is_convertible<_Tp*, nested_exception*>>>::value
    >::type;

// Attempt dynamic_cast to nested_exception and call rethrow_nested().
  template<typename _Ex>
    inline __rethrow_if_nested_cond<_Ex>
    __rethrow_if_nested_impl(const _Ex* __ptr)
    {
      if (auto __ne_ptr = dynamic_cast<const nested_exception*>(__ptr))
	__ne_ptr->rethrow_nested();
    }

// Otherwise, no effects.
  inline void
  __rethrow_if_nested_impl(const void*)
  { }

/// If @p __ex is derived from nested_exception, @p __ex.rethrow_nested().
  template<typename _Ex>
    inline void
    rethrow_if_nested(const _Ex& __ex)
    { std::__rethrow_if_nested_impl(std::__addressof(__ex)); }

// @} group exceptions
} // namespace std

} // extern "C++"

#endif // C++11

#pragma GCC visibility pop

#endif // _GLIBCXX_NESTED_EXCEPTION_H

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