1 // -*- C++ -*- 2 //===----------------------------------------------------------------------===// 3 // 4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 5 // See https://llvm.org/LICENSE.txt for license information. 6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 7 // 8 //===----------------------------------------------------------------------===// 9 10 #ifndef _LIBCPP___FLAT_MAP_UTILS_H 11 #define _LIBCPP___FLAT_MAP_UTILS_H 12 13 #include <__config> 14 #include <__type_traits/container_traits.h> 15 #include <__utility/exception_guard.h> 16 #include <__utility/forward.h> 17 #include <__utility/move.h> 18 19 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 20 # pragma GCC system_header 21 #endif 22 23 _LIBCPP_PUSH_MACROS 24 #include <__undef_macros> 25 26 #if _LIBCPP_STD_VER >= 23 27 28 _LIBCPP_BEGIN_NAMESPACE_STD 29 30 // These utilities are defined in a class instead of a namespace so that this class can be befriended more easily. 31 struct __flat_map_utils { 32 // Emplace a {key: value} into a flat_{multi}map, at the exact position that 33 // __it_key and __it_mapped point to, assuming that the key is not already present in the map. 34 // When an exception is thrown during the emplacement, the function will try its best to 35 // roll back the changes it made to the map. If it cannot roll back the changes, it will 36 // clear the map. 37 template <class _Map, class _IterK, class _IterM, class _KeyArg, class... _MArgs> 38 _LIBCPP_HIDE_FROM_ABI static typename _Map::iterator __emplace_exact_pos( 39 _Map& __map, _IterK&& __it_key, _IterM&& __it_mapped, _KeyArg&& __key, _MArgs&&... __mapped_args) { 40 auto __on_key_failed = std::__make_exception_guard([&]() noexcept { 41 using _KeyContainer = typename _Map::key_container_type; 42 if constexpr (__container_traits<_KeyContainer>::__emplacement_has_strong_exception_safety_guarantee) { 43 // Nothing to roll back! 44 } else { 45 // we need to clear both because we don't know the state of our keys anymore 46 __map.clear() /* noexcept */; 47 } 48 }); 49 auto __key_it = __map.__containers_.keys.emplace(__it_key, std::forward<_KeyArg>(__key)); 50 __on_key_failed.__complete(); 51 52 auto __on_value_failed = std::__make_exception_guard([&]() noexcept { 53 using _MappedContainer = typename _Map::mapped_container_type; 54 if constexpr (!__container_traits<_MappedContainer>::__emplacement_has_strong_exception_safety_guarantee) { 55 // we need to clear both because we don't know the state of our values anymore 56 __map.clear() /* noexcept */; 57 } else { 58 // In this case, we know the values are just like before we attempted emplacement, 59 // and we also know that the keys have been emplaced successfully. Just roll back the keys. 60 # if _LIBCPP_HAS_EXCEPTIONS 61 try { 62 # endif // _LIBCPP_HAS_EXCEPTIONS 63 __map.__containers_.keys.erase(__key_it); 64 # if _LIBCPP_HAS_EXCEPTIONS 65 } catch (...) { 66 // Now things are funky for real. We're failing to rollback the keys. 67 // Just give up and clear the whole thing. 68 // 69 // Also, swallow the exception that happened during the rollback and let the 70 // original value-emplacement exception propagate normally. 71 __map.clear() /* noexcept */; 72 } 73 # endif // _LIBCPP_HAS_EXCEPTIONS 74 } 75 }); 76 auto __mapped_it = __map.__containers_.values.emplace(__it_mapped, std::forward<_MArgs>(__mapped_args)...); 77 __on_value_failed.__complete(); 78 79 return typename _Map::iterator(std::move(__key_it), std::move(__mapped_it)); 80 } 81 82 // TODO: We could optimize this, see 83 // https://github.com/llvm/llvm-project/issues/108624 84 template <class _Map, class _InputIterator, class _Sentinel> 85 _LIBCPP_HIDE_FROM_ABI static typename _Map::size_type 86 __append(_Map& __map, _InputIterator __first, _Sentinel __last) { 87 typename _Map::size_type __num_appended = 0; 88 for (; __first != __last; ++__first) { 89 typename _Map::value_type __kv = *__first; 90 __map.__containers_.keys.insert(__map.__containers_.keys.end(), std::move(__kv.first)); 91 __map.__containers_.values.insert(__map.__containers_.values.end(), std::move(__kv.second)); 92 ++__num_appended; 93 } 94 return __num_appended; 95 } 96 }; 97 _LIBCPP_END_NAMESPACE_STD 98 99 #endif // _LIBCPP_STD_VER >= 23 100 101 _LIBCPP_POP_MACROS 102 103 #endif // #define _LIBCPP___FLAT_MAP_UTILS_H 104