[PATCH] P0604R0 add invoke_result, is_invocable etc. for C++17

[Jonathan Wakely <jwakely at redhat dot com>]

At the WG21 meeting last week we approved P0604R0 which replaces the
error-prone result_of<F(Args...)> and is_callable<F(Args...) R> APIs
with invoke_result<F, Args...> and is_invocable<F, Args...> and
is_invocable_r<R, F, Args...>. Only result_of exists in previous
standards, the rest are new for C++17.

This patch replaces the is_callable family with the new is_invocable
ones, replaces our internal __is_callable with __is_invocable (so it
can be used in C++11 mode) and also adds __invoke_result.

Most of the patch changes C++17 stuff and tests. The parts that affect
C++11 and C++14 are mostly trivial. The new invoke_result trait
revealed that there were no partial specializations of
__result_of_memobj and __result_of_memfun for const reference_wrapper
prvalues. Rather than add them I realised we already use __inv_unwrap
elsewhere, and doing so here makes the partial specializations
unnecessary.

	* include/bits/invoke.h (__invoke): Use __invoke_result instead of
	result_of, and __is_nothrow_invocable instead of
	__is_nothrow_callable.
	* include/bits/shared_ptr_base.h (__shared_ptr): Use __is_invocable
	instead of __is_callable.
	* include/std/functional (invoke): use invoke_result_t instead of
	result_of_t and is_nothrow_invocable instead of is_nothrow_callable.
	(_Not_fn): Use __invoke_result instead of result_of.
	* include/std/type_traits (__result_of_memobj, __result_of_memfun):
	Remove partial specializations for reference_wrapper types.
	(__result_of_impl): Use __inv_unwrap to strip reference_wrapper.
	(__invoke_result): Define replacement for result_of and then use it to
	define result_of.
	(__is_callable_impl, __is_callable, __is_nothrow_callable): Replace
	with __is_invocable_impl, __is_invocable, and __is_nothrow_invocable
	respectively.
	(invoke_result, invoke_result_t): Define for C++17.
	(is_callable, is_nothrow_callable): Replace with is_invocable,
	is_invocable_r, is_nothrow_invocable, and is_nothrow_invocable_r.
	(is_callable_v, is_nothrow_callable_v): Replace with is_invocable_v,
	is_invocable_r_v, is_nothrow_invocable_v, and is_nothrow_invocable_r_v.
	* include/std/variant (hash<variant<T...>>): Use is_nothrow_invocable_v
	instead of is_nothrow_callable_v.
	* testsuite/20_util/function_objects/invoke/59768.cc: Remove unused
	main function.
	* testsuite/20_util/function_objects/not_fn/1.cc: Use is_invocable
	instead of is_callable.
	* testsuite/20_util/is_callable/*: Rename directory and adjust tests
	to use new traits.
	* testsuite/20_util/is_notjrow_callable/*: Likewise.
	* testsuite/20_util/optional/hash.cc: Use is_invocable_v instead of
	is_callable.
	* testsuite/20_util/variant/hash.cc: Likewise.

Tested powerpc64le-linux, I plan to commit this to trunk tomorrow.

Attachment: patch.txt
Description: Text document