Preview: nested_exception.h
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//opt/rh/gcc-toolset-14/root/usr/include/c++/14/bits/nested_exception.h
// Nested Exception support header (nested_exception class) for -*- C++ -*-
// Copyright (C) 2009-2024 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
#if __cplusplus < 201103L
# include <bits/c++0x_warning.h>
#else
#include <bits/move.h>
#include <bits/exception_ptr.h>
extern "C++" {
namespace std _GLIBCXX_VISIBILITY(default)
{
/**
* @addtogroup exceptions
* @{
*/
/** Mixin class that stores the current exception.
*
* This type can be used via `std::throw_with_nested` to store
* the current exception nested within another exception.
*
* @headerfile exception
* @since C++11
* @see std::throw_with_nested
* @ingroup exceptions
*/
class nested_exception
{
exception_ptr _M_ptr;
public:
/// The default constructor stores the current exception (if any).
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;
/// Rethrow the stored exception, or terminate if none was stored.
[[noreturn]]
void
rethrow_nested() const
{
if (_M_ptr)
rethrow_exception(_M_ptr);
std::terminate();
}
/// Access the stored exception.
exception_ptr
nested_ptr() const noexcept
{ return _M_ptr; }
};
/// @cond undocumented
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))
{ }
};
#if __cplusplus < 201703L || ! defined __cpp_if_constexpr
// [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)
{
throw _Nested_exception<__remove_cvref_t<_Tp>>{std::forward<_Tp>(__t)};
}
template<typename _Tp>
[[noreturn]]
inline void
__throw_with_nested_impl(_Tp&& __t, false_type)
{ throw std::forward<_Tp>(__t); }
#endif
/// @endcond
/** Throw an exception that also stores the currently active exception.
*
* If `_Tp` is derived from `std::nested_exception` or is not usable
* as a base-class, throws a copy of `__t`.
* Otherwise, throws an object of an implementation-defined type derived
* from both `_Tp` and `std::nested_exception`, containing a copy of `__t`
* and the result of `std::current_exception()`.
*
* In other words, throws the argument as a new exception that contains
* the currently active exception nested within it. This is intended for
* use in a catch handler to replace the caught exception with a different
* type, while still preserving the original exception. When the new
* exception is caught, the nested exception can be rethrown by using
* `std::rethrow_if_nested`.
*
* This can be used at API boundaries, for example to catch a library's
* internal exception type and rethrow it nested with a `std::runtime_error`,
* or vice versa.
*
* @since C++11
*/
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");
#if __cplusplus >= 201703L && __cpp_if_constexpr
if constexpr (is_class_v<_Up>)
if constexpr (!is_final_v<_Up>)
if constexpr (!is_base_of_v<nested_exception, _Up>)
throw _Nested_exception<_Up>{std::forward<_Tp>(__t)};
throw std::forward<_Tp>(__t);
#else
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{});
#endif
}
#if __cplusplus < 201703L || ! defined __cpp_if_constexpr
/// @cond undocumented
// Attempt dynamic_cast to nested_exception and call rethrow_nested().
template<typename _Ex>
inline void
__rethrow_if_nested_impl(const _Ex* __ptr, true_type)
{
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*, false_type)
{ }
/// @endcond
#endif
/** Rethrow a nested exception
*
* If `__ex` contains a `std::nested_exception` object, call its
* `rethrow_nested()` member to rethrow the stored exception.
*
* After catching an exception thrown by a call to `std::throw_with_nested`
* this function can be used to rethrow the exception that was active when
* `std::throw_with_nested` was called.
*
* @since C++11
*/
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2484. rethrow_if_nested() is doubly unimplementable
// 2784. Resolution to LWG 2484 is missing "otherwise, no effects" and [...]
template<typename _Ex>
# if ! __cpp_rtti
[[__gnu__::__always_inline__]]
#endif
inline void
rethrow_if_nested(const _Ex& __ex)
{
const _Ex* __ptr = __builtin_addressof(__ex);
#if __cplusplus < 201703L || ! defined __cpp_if_constexpr
# if __cpp_rtti
using __cast = __and_<is_polymorphic<_Ex>,
__or_<__not_<is_base_of<nested_exception, _Ex>>,
is_convertible<_Ex*, nested_exception*>>>;
# else
using __cast = __and_<is_polymorphic<_Ex>,
is_base_of<nested_exception, _Ex>,
is_convertible<_Ex*, nested_exception*>>;
# endif
std::__rethrow_if_nested_impl(__ptr, __cast{});
#else
if constexpr (!is_polymorphic_v<_Ex>)
return;
else if constexpr (is_base_of_v<nested_exception, _Ex>
&& !is_convertible_v<_Ex*, nested_exception*>)
return; // nested_exception base class is inaccessible or ambiguous.
# if ! __cpp_rtti
else if constexpr (!is_base_of_v<nested_exception, _Ex>)
return; // Cannot do polymorphic casts without RTTI.
# endif
else if (auto __ne_ptr = dynamic_cast<const nested_exception*>(__ptr))
__ne_ptr->rethrow_nested();
#endif
}
/// @} group exceptions
} // namespace std
} // extern "C++"
#endif // C++11
#endif // _GLIBCXX_NESTED_EXCEPTION_H
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