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Commit cb723b8

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philnik777philnik777
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[libc++] Implement P0288R9 (move_only_function)
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‎libcxx/docs/FeatureTestMacroTable.rst

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---------------------------------------------------------- -----------------
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``__cpp_lib_modules`` ``202207L``
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---------------------------------------------------------- -----------------
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``__cpp_lib_move_only_function`` *unimplemented*
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``__cpp_lib_move_only_function`` ``202110L``
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---------------------------------------------------------- -----------------
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``__cpp_lib_optional`` ``202110L``
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---------------------------------------------------------- -----------------
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---------------------------------------------------------- -----------------
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``__cpp_lib_variant`` ``202306L``
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========================================================== =================
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‎libcxx/docs/ReleaseNotes/20.rst

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- ``std::jthread`` and ``<stop_token>`` are not guarded behind ``-fexperimental-library`` anymore
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- P2674R1: A trait for implicit lifetime types (`Github <https://github.com/llvm/llvm-project/issues/105259>`__)
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- P0429R9: A Standard ``flat_map`` is partially implemented and ``flat_map`` is provided (`Github <https://github.com/llvm/llvm-project/issues/105190>`__)
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- P0288R9 - ``move_only_function``
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Improvements and New Features
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-----------------------------

‎libcxx/docs/Status/Cxx23Papers.csv

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"`P2136R3 <https://wg21.link/P2136R3>`__","invoke_r","2021-06 (Virtual)","|Complete|","17.0",""
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"`P2166R1 <https://wg21.link/P2166R1>`__","A Proposal to Prohibit std::basic_string and std::basic_string_view construction from nullptr","2021-06 (Virtual)","|Complete|","13.0",""
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"","","","","",""
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"`P0288R9 <https://wg21.link/P0288R9>`__","``any_invocable``","2021-10 (Virtual)","","",""
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"`P0288R9 <https://wg21.link/P0288R9>`__","LWG","``move_only_function``","October 2021","|Complete|","20.0"
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"`P0798R8 <https://wg21.link/P0798R8>`__","Monadic operations for ``std::optional``","2021-10 (Virtual)","|Complete|","14.0",""
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"`P0849R8 <https://wg21.link/P0849R8>`__","``auto(x)``: ``DECAY_COPY`` in the language","2021-10 (Virtual)","|Complete|","14.0",""
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"`P1072R10 <https://wg21.link/P1072R10>`__","``basic_string::resize_and_overwrite``","2021-10 (Virtual)","|Complete|","14.0",""

‎libcxx/include/CMakeLists.txt

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__functional/is_transparent.h
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__functional/mem_fn.h
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__functional/mem_fun_ref.h
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__functional/move_only_function.h
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__functional/move_only_function_common.h
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__functional/move_only_function_impl.h
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__functional/not_fn.h
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__functional/operations.h
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__functional/perfect_forward.h

‎libcxx/include/__configuration/abi.h

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// This setting disables the addition of such artificial padding, leading to a more optimal
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// representation for several types.
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# define _LIBCPP_ABI_NO_COMPRESSED_PAIR_PADDING
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// Enable clang::trivial_abi for std::move_only_function
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# define _LIBCPP_ABI_SMALL_BUFFER_TRIVIAL_ABI
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#elif _LIBCPP_ABI_VERSION == 1
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# if !(defined(_LIBCPP_OBJECT_FORMAT_COFF) || defined(_LIBCPP_OBJECT_FORMAT_XCOFF))
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// Enable compiling copies of now inline methods into the dylib to support

‎libcxx/include/__functional/move_only_function.h

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//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP___FUNCTIONAL_MOVE_ONLY_FUNCTION_H
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#define _LIBCPP___FUNCTIONAL_MOVE_ONLY_FUNCTION_H
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#include <__config>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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# pragma GCC system_header
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#endif
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#if _LIBCPP_STD_VER >= 23 && defined(_LIBCPP_ENABLE_EXPERIMENTAL)
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// move_only_function design:
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//
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// move_only_function has a small buffer with a size of `3 * sizeof(void*)` bytes. This buffer can only be used when the
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// object that should be stored is trivially relocatable (currently only when it is trivially move constructible and
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// trivially destructible). There is also a bool in the lower bits of the vptr stored which is set when the contained
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// object is not trivially destructible.
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//
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// trivially relocatable: It would also be possible to store nothrow_move_constructible types, but that would mean
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// that move_only_function itself would not be trivially relocatable anymore. The decision to keep move_only_function
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// trivially relocatable was made because we expect move_only_function to be mostly used to store a functor. To only
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// forward functors there is C++26's std::function_ref.
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//
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// buffer size: We did a survey of six implementations from various vendors. Three of them had a buffer size of 24 bytes
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// on 64 bit systems. This also allows storing a std::string or std::vector inside the small buffer (once the compiler
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// has full support of trivially_relocatable annotations).
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//
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// trivially-destructible bit: This allows us to keep the overall binary size smaller because we don't have to store
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// a pointer to a noop function inside the vtable. It also avoids loading the vtable during destruction, potentially
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// resulting in fewer cache misses. The downside is that calling the function now also requires setting the lower bits
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// of the pointer to zero, but this is a very fast operation on modern CPUs.
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//
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// interaction with copyable_function: When converting a copyable_function into a move_only_function we want to avoid
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// wrapping the copyable_function inside the move_only_function to avoid a double indirection. Instead, we copy the
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// small buffer and use copyable_function's vtable.
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// NOLINTBEGIN(readability-duplicate-include)
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# define _LIBCPP_IN_MOVE_ONLY_FUNCTION_H
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# include <__functional/move_only_function_impl.h>
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# define _LIBCPP_MOVE_ONLY_FUNCTION_REF &
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# include <__functional/move_only_function_impl.h>
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# define _LIBCPP_MOVE_ONLY_FUNCTION_REF &&
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# include <__functional/move_only_function_impl.h>
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# define _LIBCPP_MOVE_ONLY_FUNCTION_CV const
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# include <__functional/move_only_function_impl.h>
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# define _LIBCPP_MOVE_ONLY_FUNCTION_CV const
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# define _LIBCPP_MOVE_ONLY_FUNCTION_REF &
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# include <__functional/move_only_function_impl.h>
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# define _LIBCPP_MOVE_ONLY_FUNCTION_CV const
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# define _LIBCPP_MOVE_ONLY_FUNCTION_REF &&
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# include <__functional/move_only_function_impl.h>
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# define _LIBCPP_MOVE_ONLY_FUNCTION_NOEXCEPT true
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# include <__functional/move_only_function_impl.h>
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# define _LIBCPP_MOVE_ONLY_FUNCTION_NOEXCEPT true
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# define _LIBCPP_MOVE_ONLY_FUNCTION_REF &
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# include <__functional/move_only_function_impl.h>
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# define _LIBCPP_MOVE_ONLY_FUNCTION_NOEXCEPT true
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# define _LIBCPP_MOVE_ONLY_FUNCTION_REF &&
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# include <__functional/move_only_function_impl.h>
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# define _LIBCPP_MOVE_ONLY_FUNCTION_NOEXCEPT true
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# define _LIBCPP_MOVE_ONLY_FUNCTION_CV const
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# include <__functional/move_only_function_impl.h>
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# define _LIBCPP_MOVE_ONLY_FUNCTION_NOEXCEPT true
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# define _LIBCPP_MOVE_ONLY_FUNCTION_CV const
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# define _LIBCPP_MOVE_ONLY_FUNCTION_REF &
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# include <__functional/move_only_function_impl.h>
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# define _LIBCPP_MOVE_ONLY_FUNCTION_NOEXCEPT true
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# define _LIBCPP_MOVE_ONLY_FUNCTION_CV const
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# define _LIBCPP_MOVE_ONLY_FUNCTION_REF &&
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# include <__functional/move_only_function_impl.h>
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# undef _LIBCPP_IN_MOVE_ONLY_FUNCTION_H
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// NOLINTEND(readability-duplicate-include)
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#endif // _LIBCPP_STD_VER >= 23 && defined(_LIBCPP_ENABLE_EXPERIMENTAL)
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#endif // _LIBCPP___FUNCTIONAL_MOVE_ONLY_FUNCTION_H

‎libcxx/include/__functional/move_only_function_common.h

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//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP___FUNCTIONAL_MOVE_ONLY_FUNCTION_COMMON_H
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#define _LIBCPP___FUNCTIONAL_MOVE_ONLY_FUNCTION_COMMON_H
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#include <__config>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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# pragma GCC system_header
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#endif
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_LIBCPP_BEGIN_NAMESPACE_STD
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template <class...>
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class move_only_function;
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template <class>
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inline constexpr bool __is_move_only_function_v = false;
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template <class... _Args>
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inline constexpr bool __is_move_only_function_v<move_only_function<_Args...>> = true;
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template <class _BufferT, class _ReturnT, class... _ArgTypes>
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struct _MoveOnlyFunctionTrivialVTable {
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using _CallFunc = _ReturnT(_BufferT&, _ArgTypes...);
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_CallFunc* __call_;
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};
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template <class _BufferT, class _ReturnT, class... _ArgTypes>
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struct _MoveOnlyFunctionNonTrivialVTable : _MoveOnlyFunctionTrivialVTable<_BufferT, _ReturnT, _ArgTypes...> {
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using _DestroyFunc = void(_BufferT&) noexcept;
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_DestroyFunc* __destroy_;
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};
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___FUNCTIONAL_MOVE_ONLY_FUNCTION_COMMON_H

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