From 88b1e41c2d9d2e9f5c0ae2d1a09da41d76184280 Mon Sep 17 00:00:00 2001 From: Jonathan Wakely Date: Wed, 9 May 2018 14:28:11 +0100 Subject: [PATCH] Make std::function tolerate semantically non-CopyConstructible objects To satisfy the CopyConstructible requirement a callable object stored in a std::function must behave the same when copied from a const or non-const source. If copying a non-const object doesn't produce an equivalent copy then the behaviour is undefined. But we can make our std::function more tolerant of such objects by ensuring we always copy from a const lvalue. Additionally use an if constexpr statement in the _M_get_pointer function to avoid unnecessary instantiations in the discarded branch. * include/bits/std_function.h (_Base_manager::_M_get_pointer): Use constexpr if in C++17 mode. (_Base_manager::_M_clone(_Any_data&, const _Any_data&, true_type)): Copy from const object. * testsuite/20_util/function/cons/non_copyconstructible.cc: New. From-SVN: r260080 --- libstdc++-v3/ChangeLog | 8 +++++ libstdc++-v3/include/bits/std_function.h | 17 ++++++---- .../20_util/function/cons/non_copyconstructible.cc | 39 ++++++++++++++++++++++ 3 files changed, 57 insertions(+), 7 deletions(-) create mode 100644 libstdc++-v3/testsuite/20_util/function/cons/non_copyconstructible.cc diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog index 25430fd..5d6d6eb 100644 --- a/libstdc++-v3/ChangeLog +++ b/libstdc++-v3/ChangeLog @@ -1,3 +1,11 @@ +2018-05-09 Jonathan Wakely + + * include/bits/std_function.h (_Base_manager::_M_get_pointer): + Use constexpr if in C++17 mode. + (_Base_manager::_M_clone(_Any_data&, const _Any_data&, true_type)): + Copy from const object. + * testsuite/20_util/function/cons/non_copyconstructible.cc: New. + 2018-05-08 François Dumont * src/c++11/debug.cc [_GLIBCXX_HAVE_EXECINFO_H]: Include execinfo.h. diff --git a/libstdc++-v3/include/bits/std_function.h b/libstdc++-v3/include/bits/std_function.h index 9626135..ee94d1c 100644 --- a/libstdc++-v3/include/bits/std_function.h +++ b/libstdc++-v3/include/bits/std_function.h @@ -131,8 +131,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION class _Function_base { public: - static const std::size_t _M_max_size = sizeof(_Nocopy_types); - static const std::size_t _M_max_align = __alignof__(_Nocopy_types); + static const size_t _M_max_size = sizeof(_Nocopy_types); + static const size_t _M_max_align = __alignof__(_Nocopy_types); template class _Base_manager @@ -150,10 +150,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION static _Functor* _M_get_pointer(const _Any_data& __source) { - const _Functor* __ptr = - __stored_locally? std::__addressof(__source._M_access<_Functor>()) - /* have stored a pointer */ : __source._M_access<_Functor*>(); - return const_cast<_Functor*>(__ptr); + if _GLIBCXX17_CONSTEXPR (__stored_locally) + { + const _Functor& __f = __source._M_access<_Functor>(); + return const_cast<_Functor*>(std::__addressof(__f)); + } + else // have stored a pointer + return __source._M_access<_Functor*>(); } // Clone a location-invariant function object that fits within @@ -170,7 +173,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION _M_clone(_Any_data& __dest, const _Any_data& __source, false_type) { __dest._M_access<_Functor*>() = - new _Functor(*__source._M_access<_Functor*>()); + new _Functor(*__source._M_access()); } // Destroying a location-invariant object may still require diff --git a/libstdc++-v3/testsuite/20_util/function/cons/non_copyconstructible.cc b/libstdc++-v3/testsuite/20_util/function/cons/non_copyconstructible.cc new file mode 100644 index 0000000..d2a9992 --- /dev/null +++ b/libstdc++-v3/testsuite/20_util/function/cons/non_copyconstructible.cc @@ -0,0 +1,39 @@ +// Copyright (C) 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. + +// You should have received a copy of the GNU General Public License along +// with this library; see the file COPYING3. If not see +// . + +// { dg-do run { target c++11 } } + +#include + +// This type is not CopyConstructible because copying a non-const lvalue +// will call the throwing constructor. +struct A +{ + A() = default; + A(const A&) { } // not trivial, so allocated on the heap by std::function + A(A&) { throw 1; } + void operator()() const { } +}; + +int main() +{ + const A a{}; + // Undefined, because std::function requires CopyConstructible: + std::function f(a); + // This will throw if the object is copied as non-const: + std::function g(f); +} -- 2.7.4