.. _FeatureTestMacroTable:

==========================
Feature Test Macro Support
==========================

.. contents::
   :local:

Overview
========

This file documents the feature test macros currently supported by libc++.

.. _feature-status:

Status
======

.. table:: Current Status
    :name: feature-status-table
    :widths: auto

    ========================================================== =================
    Macro Name                                                 Value
    ========================================================== =================
    **C++14**
    ----------------------------------------------------------------------------
    ``__cpp_lib_chrono_udls``                                  ``201304L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_complex_udls``                                 ``201309L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_exchange_function``                            ``201304L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_generic_associative_lookup``                   ``201304L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_integer_sequence``                             ``201304L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_integral_constant_callable``                   ``201304L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_is_final``                                     ``201402L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_is_null_pointer``                              ``201309L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_make_reverse_iterator``                        ``201402L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_make_unique``                                  ``201304L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_null_iterators``                               ``201304L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_quoted_string_io``                             ``201304L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_result_of_sfinae``                             ``201210L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_robust_nonmodifying_seq_ops``                  ``201304L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_shared_timed_mutex``                           ``201402L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_string_udls``                                  ``201304L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_transformation_trait_aliases``                 ``201304L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_transparent_operators``                        ``201210L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_tuple_element_t``                              ``201402L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_tuples_by_type``                               ``201304L``
    ---------------------------------------------------------- -----------------
    **C++17**
    ----------------------------------------------------------------------------
    ``__cpp_lib_addressof_constexpr``                          ``201603L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_allocator_traits_is_always_equal``             ``201411L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_any``                                          ``201606L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_apply``                                        ``201603L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_array_constexpr``                              ``201603L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_as_const``                                     ``201510L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_atomic_is_always_lock_free``                   ``201603L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_bool_constant``                                ``201505L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_boyer_moore_searcher``                         ``201603L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_byte``                                         ``201603L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_chrono``                                       ``201611L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_clamp``                                        ``201603L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_enable_shared_from_this``                      ``201603L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_execution``                                    *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_filesystem``                                   ``201703L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_gcd_lcm``                                      ``201606L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_hardware_interference_size``                   ``201703L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_has_unique_object_representations``            ``201606L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_hypot``                                        ``201603L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_incomplete_container_elements``                ``201505L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_invoke``                                       ``201411L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_is_aggregate``                                 ``201703L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_is_invocable``                                 ``201703L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_is_swappable``                                 ``201603L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_launder``                                      ``201606L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_logical_traits``                               ``201510L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_make_from_tuple``                              ``201606L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_map_try_emplace``                              ``201411L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_math_special_functions``                       *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_memory_resource``                              ``201603L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_node_extract``                                 ``201606L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_nonmember_container_access``                   ``201411L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_not_fn``                                       ``201603L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_optional``                                     ``201606L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_parallel_algorithm``                           *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_raw_memory_algorithms``                        ``201606L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_sample``                                       ``201603L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_scoped_lock``                                  ``201703L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_shared_mutex``                                 ``201505L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_shared_ptr_arrays``                            ``201611L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_shared_ptr_weak_type``                         ``201606L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_string_view``                                  ``201606L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_to_chars``                                     *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_transparent_operators``                        ``201510L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_type_trait_variable_templates``                ``201510L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_uncaught_exceptions``                          ``201411L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_unordered_map_try_emplace``                    ``201411L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_variant``                                      ``202102L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_void_t``                                       ``201411L``
    ---------------------------------------------------------- -----------------
    **C++20**
    ----------------------------------------------------------------------------
    ``__cpp_lib_array_constexpr``                              ``201811L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_assume_aligned``                               ``201811L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_atomic_flag_test``                             ``201907L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_atomic_float``                                 *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_atomic_lock_free_type_aliases``                ``201907L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_atomic_ref``                                   ``201806L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_atomic_shared_ptr``                            *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_atomic_value_initialization``                  ``201911L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_atomic_wait``                                  ``201907L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_barrier``                                      ``201907L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_bind_front``                                   ``201907L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_bit_cast``                                     ``201806L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_bitops``                                       ``201907L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_bounded_array_traits``                         ``201902L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_char8_t``                                      ``201907L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_concepts``                                     ``202002L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constexpr_algorithms``                         ``201806L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constexpr_complex``                            ``201711L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constexpr_dynamic_alloc``                      ``201907L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constexpr_functional``                         ``201907L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constexpr_iterator``                           ``201811L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constexpr_memory``                             ``201811L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constexpr_numeric``                            ``201911L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constexpr_string``                             ``201907L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constexpr_string_view``                        ``201811L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constexpr_tuple``                              ``201811L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constexpr_utility``                            ``201811L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constexpr_vector``                             ``201907L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_coroutine``                                    ``201902L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_destroying_delete``                            ``201806L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_endian``                                       ``201907L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_erase_if``                                     ``202002L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_execution``                                    *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_format``                                       ``202110L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_format_uchar``                                 ``202311L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_generic_unordered_lookup``                     ``201811L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_int_pow2``                                     ``202002L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_integer_comparison_functions``                 ``202002L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_interpolate``                                  ``201902L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_is_constant_evaluated``                        ``201811L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_is_layout_compatible``                         *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_is_nothrow_convertible``                       ``201806L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_is_pointer_interconvertible``                  *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_jthread``                                      ``201911L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_latch``                                        ``201907L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_list_remove_return_type``                      ``201806L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_math_constants``                               ``201907L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_move_iterator_concept``                        ``202207L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_polymorphic_allocator``                        ``201902L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_ranges``                                       ``202207L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_remove_cvref``                                 ``201711L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_semaphore``                                    ``201907L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_shared_ptr_arrays``                            ``201707L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_shift``                                        ``201806L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_smart_ptr_for_overwrite``                      *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_source_location``                              ``201907L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_span``                                         ``202002L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_ssize``                                        ``201902L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_starts_ends_with``                             ``201711L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_string_view``                                  ``201803L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_syncbuf``                                      ``201803L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_three_way_comparison``                         ``201907L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_to_address``                                   ``201711L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_to_array``                                     ``201907L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_type_identity``                                ``201806L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_unwrap_ref``                                   ``201811L``
    ---------------------------------------------------------- -----------------
    **C++23**
    ----------------------------------------------------------------------------
    ``__cpp_lib_adaptor_iterator_pair_constructor``            ``202106L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_allocate_at_least``                            ``202302L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_associative_heterogeneous_erasure``            *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_bind_back``                                    ``202202L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_byteswap``                                     ``202110L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constexpr_bitset``                             ``202207L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constexpr_charconv``                           ``202207L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constexpr_cmath``                              *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constexpr_memory``                             ``202202L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constexpr_typeinfo``                           ``202106L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_containers_ranges``                            ``202202L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_expected``                                     ``202211L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_format_ranges``                                ``202207L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_formatters``                                   *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_forward_like``                                 ``202207L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_invoke_r``                                     ``202106L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_ios_noreplace``                                ``202207L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_is_scoped_enum``                               ``202011L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_mdspan``                                       ``202207L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_modules``                                      ``202207L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_move_only_function``                           *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_optional``                                     ``202110L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_out_ptr``                                      ``202106L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_print``                                        ``202207L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_ranges_as_const``                              *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_ranges_as_rvalue``                             ``202207L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_ranges_chunk``                                 *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_ranges_chunk_by``                              ``202202L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_ranges_contains``                              ``202207L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_ranges_find_last``                             ``202207L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_ranges_iota``                                  *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_ranges_join_with``                             *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_ranges_repeat``                                ``202207L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_ranges_slide``                                 *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_ranges_starts_ends_with``                      ``202106L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_ranges_to_container``                          ``202202L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_ranges_zip``                                   *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_reference_from_temporary``                     *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_spanstream``                                   *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_stacktrace``                                   *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_stdatomic_h``                                  ``202011L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_string_contains``                              ``202011L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_string_resize_and_overwrite``                  ``202110L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_to_underlying``                                ``202102L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_tuple_like``                                   *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_unreachable``                                  ``202202L``
    ---------------------------------------------------------- -----------------
    **C++26**
    ----------------------------------------------------------------------------
    ``__cpp_lib_associative_heterogeneous_insertion``          *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_atomic_min_max``                               *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_bind_front``                                   ``202306L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_bitset``                                       ``202306L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constexpr_new``                                *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_constrained_equality``                         *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_copyable_function``                            *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_debugging``                                    *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_default_template_type_for_algorithm_values``   *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_format_path``                                  *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_freestanding_algorithm``                       *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_freestanding_array``                           *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_freestanding_cstring``                         *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_freestanding_expected``                        *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_freestanding_mdspan``                          *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_freestanding_optional``                        *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_freestanding_string_view``                     *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_freestanding_variant``                         *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_fstream_native_handle``                        ``202306L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_function_ref``                                 *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_generate_random``                              *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_hazard_pointer``                               *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_inplace_vector``                               *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_is_virtual_base_of``                           *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_is_within_lifetime``                           *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_linalg``                                       *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_mdspan``                                       ``202406L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_optional_range_support``                       *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_out_ptr``                                      ``202311L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_philox_engine``                                *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_ranges_concat``                                *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_ratio``                                        ``202306L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_rcu``                                          *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_reference_wrapper``                            ``202403L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_saturation_arithmetic``                        ``202311L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_senders``                                      *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_smart_ptr_owner_equality``                     *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_span_at``                                      ``202311L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_span_initializer_list``                        ``202311L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_sstream_from_string_view``                     ``202306L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_string_view``                                  ``202403L``
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_submdspan``                                    *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_text_encoding``                                *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_to_chars``                                     *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_to_string``                                    *unimplemented*
    ---------------------------------------------------------- -----------------
    ``__cpp_lib_tuple_like``                                   *unimplemented*
    ========================================================== =================