Implement ranges::replace_copy

[miscco]

This implements ranges_copy. There is some bug my brain autocorrect away. Will look at it later in the evening

[StephanTLavavej]

The compiler error is:

C:\agent\_work\1\s\tests\std\tests\P0896R4_ranges_alg_replace_copy\test.cpp(35,17): error: no matching function for call to object of type 'const std::ranges::_Replace_copy_fn'
                replace_copy(wrapped_input.begin(), wrapped_input.end(), Write{output}, 47, P{47, 1}, get_second);
                ^~~~~~~~~~~~
C:/agent/_work/1/s/tests/std/include\range_algorithm_support.hpp(603,32): note: in instantiation of function template specialization 'instantiator::call<test::range<std::input_iterator_tag, const std::pair<int, int>, test::Sized::no, test::CanDifference::no, test::Common::no, test::CanCompare::no, test::ProxyRef::no>, test::iterator<std::input_iterator_tag, std::pair<int, int>, test::CanDifference::no, test::CanCompare::no, test::ProxyRef::no, test::IsWrapped::yes> >' requested here
        Continuation::template call<Args...,
                               ^
C:/agent/_work/1/s/tests/std/include\range_algorithm_support.hpp(770,32): note: in instantiation of function template specialization 'with_writable_iterators<instantiator, std::pair<int, int> >::call<test::range<std::input_iterator_tag, const std::pair<int, int>, test::Sized::no, test::CanDifference::no, test::Common::no, test::CanCompare::no, test::ProxyRef::no> >' requested here
        Continuation::template call<Args...,
                               ^
C:/agent/_work/1/s/tests/std/include\range_algorithm_support.hpp(945,83): note: in instantiation of function template specialization 'with_input_ranges<with_writable_iterators<instantiator, std::pair<int, int> >, const std::pair<int, int> >::call<>' requested here
    with_input_ranges<with_writable_iterators<Instantiator, Element2>, Element1>::call();
                                                                                  ^
C:\agent\_work\1\s\tests\std\tests\P0896R4_ranges_alg_replace_copy\test.cpp(55,20): note: in instantiation of function template specialization 'test_in_write<instantiator, const std::pair<int, int>, std::pair<int, int> >' requested here
    STATIC_ASSERT((test_in_write<instantiator, P const, P>(), true));
                   ^
D:\build\x64\out\inc\algorithm(3080,50): note: candidate template ignored: constraints not satisfied [with _It = test::iterator<std::input_iterator_tag, const std::pair<int, int>, test::CanDifference::no, test::CanCompare::no, test::ProxyRef::no, test::IsWrapped::yes>, _Se = test::sentinel<const std::pair<int, int>, test::IsWrapped::yes>, _Ty1 = int, _Ty2 = std::pair<int, int>, _Out = test::iterator<std::input_iterator_tag, std::pair<int, int>, test::CanDifference::no, test::CanCompare::no, test::ProxyRef::no, test::IsWrapped::yes>, _Pj = get_nth_fn<1>]
        constexpr replace_copy_result<_It, _Out> operator()(
                                                 ^
D:\build\x64\out\inc\algorithm(3076,86): note: because 'output_iterator<test::iterator<std::input_iterator_tag, std::pair<int, int>, test::CanDifference::no, test::CanCompare::no, test::ProxyRef::no, test::IsWrapped::yes>, const std::pair<int, int> &>' evaluated to false
        template <input_iterator _It, sentinel_for<_It> _Se, class _Ty1, class _Ty2, output_iterator<const _Ty2&> _Out,
                                                                                     ^
D:\build\x64\out\inc\xutility(844,9): note: because '*__i++ = static_cast<_Ty &&>(__t)' would be invalid: indirection requires pointer operand ('void' invalid)
        *__i++ = static_cast<_Ty&&>(__t);
        ^

The template machinery here is almost beyond my comprehension, but I observe that (1) your test differs from the other tests currently using test_in_write in that its instantiator actually verifies the indirectly_writable concept, and (2) with_writable_iterators appears to pass iterator<input, MEOW> which doesn't seem correct:

STL/tests/std/include/range_algorithm_support.hpp

Lines 603 to 606 in 5be7d49

	Continuation::template call<Args...,
	iterator<input, Element, CanDifference::no, CanCompare::no, ProxyRef::no>>();
	Continuation::template call<Args...,
	iterator<input, Element, CanDifference::no, CanCompare::no, ProxyRef::yes>>();

I'm not sure if this analysis is correct.

[miscco]

I am wondering whether the output_iterator<const _Ty2&> _Out really makes sense. Especially given that all other algorithms (including copy) only require weakly_incrementable _Out.

@CaseyCarter can you remember why these two (and the remove_copy_*) are different?

[miscco]

Dropping in favor of #983