When using -std=c++17 (or above), `unary_function` and `binary_function` should not exist in the `std` namespace, but the following code still compiles: #include <functional> struct F : std::binary_function<int, int, int> {};
This is not a bug. The names are still reserved for use by the implementation, so we can do whatever we want with them. Libstdc++ chooses to use those names to define classes identical to the ones of the same name defined by previous standards. Removing those classes would have ABI impact, and so I am opposed to removing them.
*** Bug 91383 has been marked as a duplicate of this bug. ***
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>: https://gcc.gnu.org/g:de196e5dd8ea4d0ed01a8c265afdd3676e27545b commit r12-6581-gde196e5dd8ea4d0ed01a8c265afdd3676e27545b Author: Jonathan Wakely <jwakely@redhat.com> Date: Tue Jan 11 18:42:38 2022 +0000 libstdc++: Add attribute to features deprecated in C++17 [PR91260] There are a lot of things in the C++ standard library which were deprecated in C++11, and more in C++17. Some of them were removed after deprecation and are no longer present in the standard at all. We have not removed these from libstdc++ because keeping them as non-standard extensions is conforming, and avoids gratuitously breaking user code, and in some cases we need to keep using them to avoid ABI changes. But we should at least give a warning for using them. That has not been done previously because of the library's own uses of them (e.g. the std::iterator class template used as a base class). This adds deprecated attributes to the relevant components, and then goes through the whole library to add diagnostic pragmas where needed to suppress warnings about our internal uses of them. The tests are updated to either expect the additional warnings, or to suppress them where we aren't interested in them. libstdc++-v3/ChangeLog: PR libstdc++/91260 PR libstdc++/91383 PR libstdc++/95065 * include/backward/binders.h (bind1st, bind2nd): Add deprecated attribute. * include/bits/refwrap.h (_Maybe_unary_or_binary_function): Disable deprecated warnings for base classes. (_Reference_wrapper_base): Likewise. * include/bits/shared_ptr_base.h (_Sp_owner_less): Likewise. * include/bits/stl_bvector.h (_Bit_iterator_base): Likewise. * include/bits/stl_function.h (unary_function, binary_function): Add deprecated attribute. (unary_negate, not1, binary_negate, not2, ptr_fun) (pointer_to_unary_function, pointer_to_binary_function) (mem_fun_t, const_mem_fun_t, mem_fun_ref_t, const_mem_fun_ref_t) (mem_fun1_t, const_mem_fun1_t, mem_fun_ref1_t) (const_mem_fun1_ref_t, mem_fun, mem_fun_ref): Add deprecated attributes. * include/bits/stl_iterator.h: Disable deprecated warnings for std::iterator base classes. * include/bits/stl_iterator_base_types.h (iterator): Add deprecated attribute. * include/bits/stl_map.h (map::value_compare): Disable deprecated warnings for base class. * include/bits/stl_multimap.h (multimap::value_compare): Likewise. * include/bits/stl_raw_storage_iter.h (raw_storage_iterator): Add deprecated attribute. * include/bits/stl_tempbuf.h (get_temporary_buffer): Likewise. * include/bits/stream_iterator.h: Disable deprecated warnings. * include/bits/streambuf_iterator.h: Likewise. * include/ext/bitmap_allocator.h: Remove unary_function base classes. * include/ext/functional: Disable deprecated warnings. * include/ext/rope: Likewise. * include/ext/throw_allocator.h: Likewise. * include/std/type_traits (result_of): Add deprecated attribute. * include/tr1/functional: Disable deprecated warnings. * include/tr1/functional_hash.h: Likewise. * testsuite/20_util/function_objects/binders/1.cc: Add -Wno-disable-deprecations. * testsuite/20_util/function_objects/binders/3113.cc: Likewise. * testsuite/20_util/function_objects/constexpr.cc: Add dg-warning. * testsuite/20_util/raw_storage_iterator/base.cc: Likewise. * testsuite/20_util/raw_storage_iterator/dr2127.cc: Likewise. * testsuite/20_util/raw_storage_iterator/requirements/base_classes.cc: Likewise. * testsuite/20_util/raw_storage_iterator/requirements/explicit_instantiation/1.cc: Likewise. * testsuite/20_util/raw_storage_iterator/requirements/typedefs.cc: Likewise. * testsuite/20_util/reference_wrapper/24803.cc: Likewise. * testsuite/20_util/reference_wrapper/typedefs.cc: Enable for C++20 and check for absence of nested types. * testsuite/20_util/shared_ptr/comparison/less.cc: Remove std::binary_function base class. * testsuite/20_util/temporary_buffer.cc: Add dg-warning. * testsuite/21_strings/basic_string/cons/char/69092.cc: Remove std::iterator base class. * testsuite/24_iterators/back_insert_iterator/requirements/base_classes.cc: Likewise. * testsuite/24_iterators/front_insert_iterator/requirements/base_classes.cc: Likewise. * testsuite/24_iterators/insert_iterator/requirements/base_classes.cc: Likewise. * testsuite/24_iterators/istream_iterator/requirements/base_classes.cc: Likewise. * testsuite/24_iterators/istreambuf_iterator/92285.cc: Likewise. * testsuite/24_iterators/istreambuf_iterator/requirements/base_classes.cc: Likewise. * testsuite/24_iterators/ostream_iterator/requirements/base_classes.cc: Likewise. * testsuite/24_iterators/ostreambuf_iterator/requirements/base_classes.cc: Likewise. * testsuite/24_iterators/reverse_iterator/requirements/base_classes.cc: Likewise. * testsuite/25_algorithms/copy/34595.cc: Likewise. * testsuite/25_algorithms/minmax/3.cc: Remove std::binary_function base class. * testsuite/25_algorithms/all_of/requirements/explicit_instantiation/2.cc: Disable deprecated warnings. * testsuite/25_algorithms/all_of/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/any_of/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/any_of/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/copy_if/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/copy_if/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/count_if/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/count_if/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/find_end/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/find_end/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/find_first_of/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/find_first_of/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/find_if/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/find_if/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/find_if_not/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/find_if_not/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/for_each/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/for_each/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/is_partitioned/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/is_partitioned/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/is_permutation/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/is_permutation/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/none_of/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/none_of/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/partition/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/partition/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/partition_copy/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/partition_copy/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/partition_point/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/partition_point/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/random_shuffle/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/random_shuffle/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/remove_copy_if/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/remove_copy_if/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/remove_if/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/remove_if/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/replace_copy_if/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/replace_copy_if/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/replace_if/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/replace_if/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/search/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/search/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/search_n/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/search_n/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/stable_partition/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/stable_partition/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/25_algorithms/transform/requirements/explicit_instantiation/2.cc: Likewise. * testsuite/25_algorithms/transform/requirements/explicit_instantiation/pod.cc: Likewise. * testsuite/27_io/basic_filebuf/underflow/wchar_t/9178.cc: Add dg-warning. * testsuite/ext/pb_ds/example/priority_queue_erase_if.cc: Likewise. * testsuite/ext/pb_ds/example/priority_queue_split_join.cc: Likewise. * testsuite/tr1/3_function_objects/reference_wrapper/typedefs.cc: Disable deprecated warnings. * testsuite/tr1/6_containers/hash/requirements/base_classes.cc: Likewise. * testsuite/util/regression/trait/erase_if_fn.hpp: Remove std::unary_function base classes. * testsuite/util/testsuite_iterators.h (output_iterator_wrapper): Remove std::iterator base classes.
For GCC 12 those types will still exist (because as explained above, that is allowed by the standard) but they will give -Wdeprecated warnings.