C++17 idioms and their C++20 spellings

The C++17 way of writing something, the C++20 name for the same thing, and the feature-test macro that says whether the toolchain has it. Test the macro, not the compiler version: library features arrive at different times in libstdc++, libc++ and MSVC.

C++17 idiom	C++20 spelling	Feature-test macro
a std::thread joined by hand or in a destructor	std::jthread, std::stop_token	__cpp_lib_jthread
the erase-remove idiom	std::erase_if	__cpp_lib_erase_if
m.find(k) != m.end()	m.contains(k)	none; test __cplusplus >= 202002L (_MSVC_LANG on MSVC)
streams and snprintf	std::format	__cpp_lib_format
a pointer plus a length	std::span	__cpp_lib_span
find_if with a lambda, the map-to-vector dance	ranges and views	__cpp_lib_ranges
the detection idiom, static_assert on a trait	concepts and requires	__cpp_concepts
__FILE__ and __LINE__ through a macro	std::source_location	__cpp_lib_source_location

Feature-test macros live in <version>; include it before testing any __cpp_lib_* name.

Source: https://mkhomutov.github.io/going-unmanaged/K-the-standards-catalogue/