nested_exception.h

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

// Copyright (C) 2009, 2010, 2011 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)

#ifndef __GXX_EXPERIMENTAL_CXX0X__
# include <bits/c++0x_warning.h>
#else

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

#if ATOMIC_INT_LOCK_FREE < 2
#  error This platform does not support exception propagation.
#endif

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&) = default;

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

    virtual ~nested_exception() noexcept;

    void
    rethrow_nested() const __attribute__ ((__noreturn__))
    { rethrow_exception(_M_ptr); }

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

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

  template<typename _Ex>
    struct __get_nested_helper
    {
      static const nested_exception*
      _S_get(const _Ex& __ex)
      { return dynamic_cast<const nested_exception*>(&__ex); }
    };

  template<typename _Ex>
    struct __get_nested_helper<_Ex*>
    {
      static const nested_exception*
      _S_get(const _Ex* __ex)
      { return dynamic_cast<const nested_exception*>(__ex); }
    };

  template<typename _Ex>
    inline const nested_exception*
    __get_nested_exception(const _Ex& __ex)
    { return __get_nested_helper<_Ex>::_S_get(__ex); }

  template<typename _Ex>
    void
    __throw_with_nested(_Ex&&, const nested_exception* = 0)
    __attribute__ ((__noreturn__));

  template<typename _Ex>
    void
    __throw_with_nested(_Ex&&, ...) __attribute__ ((__noreturn__));

  // This function should never be called, but is needed to avoid a warning
  // about ambiguous base classes when instantiating throw_with_nested<_Ex>()
  // with a type that has an accessible nested_exception base.
  template<typename _Ex>
    inline void
    __throw_with_nested(_Ex&& __ex, const nested_exception*)
    { throw __ex; }

  template<typename _Ex>
    inline void
    __throw_with_nested(_Ex&& __ex, ...)
    { throw _Nested_exception<_Ex>(static_cast<_Ex&&>(__ex)); }
  
  template<typename _Ex>
    void
    throw_with_nested(_Ex __ex) __attribute__ ((__noreturn__));

  /// If @p __ex is derived from nested_exception, @p __ex. 
  /// Else, an implementation-defined object derived from both.
  template<typename _Ex>
    inline void
    throw_with_nested(_Ex __ex)
    {
      if (__get_nested_exception(__ex))
        throw __ex;
      __throw_with_nested(static_cast<_Ex&&>(__ex), &__ex);
    }

  /// If @p __ex is derived from nested_exception, @p __ex.rethrow_nested().
  template<typename _Ex>
    inline void
    rethrow_if_nested(const _Ex& __ex)
    {
      if (const nested_exception* __nested = __get_nested_exception(__ex))
        __nested->rethrow_nested();
    }

  /// Overload, See N2619
  inline void
  rethrow_if_nested(const nested_exception& __ex)
  { __ex.rethrow_nested(); }

  // @} group exceptions
} // namespace std

} // extern "C++"

#endif // __GXX_EXPERIMENTAL_CXX0X__

#pragma GCC visibility pop

#endif // _GLIBCXX_NESTED_EXCEPTION_H