C++ standard libraries extensions, version 3

From cppreference.com

Version 3 of the C++ Extensions for Library Fundamentals, ISO/IEC TS 19568:2024, defines the following new components for the C++ standard library, in addition to those defined in version 1 and version 2.

Components merged into C++17/20 and the following components are removed in LFTS v3:

std::experimental::make_array,
std::experimental::erased_type,
std::experimental::packaged_task, and
std::experimental::promise.

Scope guard

Feature test macros

Defined in header `<experimental/memory_resource>`
__cpp_lib_experimental_memory_resources	a value of at least `201803` indicates that `resource_adaptor` is supported (macro constant)
Defined in header `<experimental/functional>`
__cpp_lib_experimental_function_polymorphic_allocator	a value of at least `202211` indicates that `std::pmr::polymorphic_allocator<>` is used for `std::experimental::function` (macro constant)
Defined in header `<experimental/scope>`
__cpp_lib_experimental_scope	a value of at least `201902` indicates that the scope guards are supported (macro constant)

Notes

The value of __cpp_lib_experimental_memory_resources has been increased in LFTS v3, because the design of resource_adaptor is rebased onto std::pmr::memory_resource.