[libc++][ranges] implement `std::ranges::unique{_copy}`

[huixie90]

Summary

implement std::ranges::unique and std::ranges::unique_copy

Several changes:

1. implement std::ranges::unique that delegates to std::unique

2. fix classic std::unique_copy does not work with output iterator that satisfies both InputIterator and OutputIterator requirements.

background: The classic implementation does tag dispatch on the iteartor_category of the output iterator and uses output_iterator_tag as a fallback. However, if the user passes an output iterator that satisfy both
InputIterator and OutputIterator requirement, the iteartor_category is likely to be input_iteartor_tag and input_iteartor_tag does not derive from output_iterator_tag. So the fallback case would not work.

See this example where msvc stl correctly implemented and libc++ errors out
https://godbolt.org/z/7shKshEPa

The fix to the classic algorithm is strictly following the wording

If InputIterator meets the Cpp17ForwardIterator requirements, then there are no additional requirements for T.

Having an overload that takes __reread_from_input_tag, which does auto prev = in; comp(*prev, *in)

Otherwise, if OutputIterator meets the Cpp17ForwardIterator requirements and its value type is the same as T, then T meets the Cpp17CopyAssignable (Table 33) requirements.

Having an overload that takes __reread_from_output_tag, which does comp(*out, *in)

Otherwise, T meets both the Cpp17CopyConstructible (Table 31) and Cpp17CopyAssignable requirements.

Having an overload that takes __read_from_tmp_value_tag, which does value_type tmp = *in; ++in; comp(tmp, *in)

3. implement std::ranges::unique_copy, which reuses the implementation above, but slightly different dispatching condition as ranges version has slightly different requires constraints.

Also I believe the std::ranges::unique_copy is incorrectly constrained. More specifically, the intent of the constraint (input_­iterator<O> && same_­as<iter_value_t<I>, iter_value_t<O>>) was to allow implementations to write comp(*in ,*out) (ignore std::invoke and projection for now). However, I and O having the same value_type is not enough to allow comp(*in ,*out), because that expression only uses the iter_reference_t of the I and O, instead of the iter_value_t. See discussion here
https://discord.com/channels/737189251069771789/737189251497721887/1000875764650094692

But anyway, I decided that in this patch, implement what exactly in the spec and bring up the issue in LWG later.

[huixie90]

fix CI

[huixie90]

refactor unique_copy

[huixie90]

implement unique_copy

[var-const]

LGTM, leaving the final approval to @ldionne.

libcxx/include/__algorithm/adjacent_find.h

49 ↗

(On Diff #447367)

Nit: move?

libcxx/include/__algorithm/unique.h

39 ↗

(On Diff #447367)

Nit: I'd move the increment back into its own line, otherwise there's a little too much going on on this line.

libcxx/include/__algorithm/unique_copy.h

80 ↗

(On Diff #447367)

Perhaps InputOrOutputIterator?

libcxx/test/std/algorithms/alg.modifying.operations/alg.unique/ranges_unique.pass.cpp

129 ↗

(On Diff #447367)

Optional: maybe check a single-element range for good measure?

libcxx/test/std/algorithms/ranges_robust_against_dangling.pass.cpp

91

Please also update test/std/algorithms/ranges_result_alias_declarations.compile.pass.cpp.

[huixie90]

addresss feedback

libcxx/include/__algorithm/unique_copy.h

80 ↗

(On Diff #447367)

Renamed to InputAndOutputIterator

[huixie90]

rebase

[huixie90]

• finalise ranges::remove_copy{_if}

[huixie90]

got patch number wrong

[ldionne]

Thanks a lot for the patch @huixie90! Since you're on vacation, @var-const can you please commandeer to finish this up? LGTM w/ comments applied.

libcxx/include/__algorithm/adjacent_find.h

28–38 ↗

(On Diff #448350)

How about this? It's equivalent, but I find it slightly easier to read.

Non-blocking if you disagree.

libcxx/include/__algorithm/ranges_unique_copy.h

95 ↗

(On Diff #448350)

FWIW this formatting is really hard to read for me, I assume it's produced by clang-format?

libcxx/include/__algorithm/unique_copy.h

37 ↗

(On Diff #448350)

I think we should call it __unique_copy instead for consistency with other algorithms (even though I understand we're passing an additional tag parameter).

47 ↗

(On Diff #448350)

Do we have a test for calling unique_copy with a value_type that is not copyable? IIUC that would be valid when the input range is at least a forward_iterator.

[huixie90]

address review feedback

[huixie90]

Also thanks to @Quuxplusone who contacted me and spotted that I missed an if constexpr in ranges::unique_copy and an unnecessary next call in adjacent_find

libcxx/include/__algorithm/adjacent_find.h

28–38 ↗

(On Diff #448350)

Yes your suggestion is easier to read

libcxx/include/__algorithm/ranges_unique_copy.h

95 ↗

(On Diff #448350)

yes it is done by clang-format. yes it is really hard to read. I will try manually formatting it.

libcxx/include/__algorithm/unique_copy.h

37 ↗

(On Diff #448350)

sure will rename. the direct reason I didn't use __unique_copy at the first place is that I used this name for the namespace few lines above. But I can rename that namespace

47 ↗

(On Diff #448350)

good spot. we do have tests in ranges version but no tests in classic

libcxx/docs/Status/RangesAlgorithms.csv

 Write,copy_backward,Nikolas Klauser,`D122982 <https://llvm.org/D122982>`_,✅
 Write,move,Nikolas Klauser,`D126616 <https://llvm.org/D126616>`_,✅
 Write,move_backward,Nikolas Klauser,`D126616 <https://llvm.org/D126616>`_,✅
 Write,fill,Nikolas Klauser,`D123462 <https://llvm.org/D123462>`_,✅
 Write,fill_n,Nikolas Klauser,`D123462 <https://llvm.org/D123462>`_,✅
 Write,transform,Nikolas Klauser,`D122173 <https://llvm.org/D122173>`_,✅
 Write,generate,Nikolas Klauser,n/a,Not started
 Write,generate_n,Nikolas Klauser,n/a,Not started
-Write,remove_copy,Nikolas Klauser,n/a,Not started
-Write,remove_copy_if,Nikolas Klauser,n/a,Not started
+Write,remove_copy,Nikolas Klauser,`D130599 <https://llvm.org/D130599>`_,✅
+Write,remove_copy_if,Nikolas Klauser,`D130599 <https://llvm.org/D130599>`_,✅
 Write,replace,Nikolas Klauser,`D126283 <https://llvm.org/D126283>`_,✅
 Write,replace_if,Nikolas Klauser,`D126283 <https://llvm.org/D126283>`_,✅
 Write,replace_copy,Nikolas Klauser,`D129806 <https://llvm.org/D129806>`_,Under review
 Write,replace_copy_if,Nikolas Klauser,`D129806 <https://llvm.org/D129806>`_,Under review
 Write,swap_ranges,Nikolas Klauser,`D116303 <https://llvm.org/D116303>`_,✅
 Write,reverse_copy,Nikolas Klauser,`D127211 <https://llvm.org/D127211>`_,✅
 Write,rotate_copy,Nikolas Klauser,`D127211 <https://llvm.org/D127211>`_,✅
 Write,sample,Not assigned,n/a,Not started

libcxx/include/__algorithm/ranges_remove_copy.h

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP___ALGORITHM_RANGES_REMOVE_COPY_H
 #define _LIBCPP___ALGORITHM_RANGES_REMOVE_COPY_H
 
 #include <__algorithm/in_out_result.h>
-#include <__algorithm/make_projected.h>
-#include <__algorithm/remove_copy.h>
+#include <__algorithm/ranges_remove_copy_if.h>
 #include <__config>
 #include <__functional/identity.h>
 #include <__functional/invoke.h>
 #include <__functional/ranges_operations.h>
 #include <__iterator/concepts.h>
-#include <__iterator/iterator_traits.h>
 #include <__iterator/projected.h>
 #include <__ranges/access.h>
 #include <__ranges/concepts.h>
 #include <__ranges/dangling.h>
-#include <__utility/forward.h>
 #include <__utility/move.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 #if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace ranges {
 
 template <class _InIter, class _OutIter>
 using remove_copy_result = in_out_result<_InIter, _OutIter>;
 
 namespace __remove_copy {
 
   struct __fn {
-
-  template <input_iterator _InIter, sentinel_for<_InIter> _Sent, weakly_incrementable _OutIter, class _Type,
+    template <input_iterator _InIter,
+              sentinel_for<_InIter> _Sent,
+              weakly_incrementable _OutIter,
+              class _Type,
               class _Proj = identity>
       requires indirectly_copyable<_InIter, _OutIter> &&
                indirect_binary_predicate<ranges::equal_to, projected<_InIter, _Proj>, const _Type*>
-  _LIBCPP_HIDE_FROM_ABI constexpr
-  remove_copy_result<_InIter, _OutIter>
+    _LIBCPP_HIDE_FROM_ABI constexpr remove_copy_result<_InIter, _OutIter>
     operator()(_InIter __first, _Sent __last, _OutIter __result, const _Type& __value, _Proj __proj = {}) const {
-    // TODO: implement
-    (void)__first; (void)__last; (void)__result; (void)__value; (void)__proj;
-    return {};
+      auto __pred = [&](auto&& __val) { return __value == __val; };
+      return ranges::__remove_copy_if_impl(std::move(__first), std::move(__last), std::move(__result), __pred, __proj);
     }
 
     template <input_range _Range, weakly_incrementable _OutIter, class _Type, class _Proj = identity>
       requires indirectly_copyable<iterator_t<_Range>, _OutIter> &&
                indirect_binary_predicate<ranges::equal_to, projected<iterator_t<_Range>, _Proj>, const _Type*>
-  _LIBCPP_HIDE_FROM_ABI constexpr
-  remove_copy_result<borrowed_iterator_t<_Range>, _OutIter>
+    _LIBCPP_HIDE_FROM_ABI constexpr remove_copy_result<borrowed_iterator_t<_Range>, _OutIter>
     operator()(_Range&& __range, _OutIter __result, const _Type& __value, _Proj __proj = {}) const {
-    // TODO: implement
-    (void)__range; (void)__result; (void)__value; (void)__proj;
-    return {};
+      auto __pred = [&](auto&& __val) { return __value == __val; };
+      return ranges::__remove_copy_if_impl(
+          ranges::begin(__range), ranges::end(__range), std::move(__result), __pred, __proj);
     }
-
   };
 
 } // namespace __remove_copy
 
 inline namespace __cpo {
   inline constexpr auto remove_copy = __remove_copy::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
 
 #endif // _LIBCPP___ALGORITHM_RANGES_REMOVE_COPY_H

libcxx/include/__algorithm/ranges_remove_copy_if.h

 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace ranges {
 
 template <class _InIter, class _OutIter>
 using remove_copy_if_result = in_out_result<_InIter, _OutIter>;
 
+template <class _InIter, class _Sent, class _OutIter, class _Proj, class _Pred>
+_LIBCPP_HIDE_FROM_ABI constexpr in_out_result<_InIter, _OutIter>
+__remove_copy_if_impl(_InIter __first, _Sent __last, _OutIter __result, _Pred& __pred, _Proj& __proj) {
+  for (; __first != __last; ++__first) {
+    if (!std::invoke(__pred, std::invoke(__proj, *__first))) {
+      *__result = *__first;
+      ++__result;
+    }
+  }
+  return {std::move(__first), std::move(__result)};
+}
+
 namespace __remove_copy_if {
 
   struct __fn {
-
-  template <input_iterator _InIter, sentinel_for<_InIter> _Sent, weakly_incrementable _OutIter,
-            class _Proj = identity, indirect_unary_predicate<projected<_InIter, _Proj>> _Pred>
+    template <input_iterator _InIter,
+              sentinel_for<_InIter> _Sent,
+              weakly_incrementable _OutIter,
+              class _Proj = identity,
+              indirect_unary_predicate<projected<_InIter, _Proj>> _Pred>
       requires indirectly_copyable<_InIter, _OutIter>
-  _LIBCPP_HIDE_FROM_ABI constexpr
-  remove_copy_if_result<_InIter, _OutIter>
+    _LIBCPP_HIDE_FROM_ABI constexpr remove_copy_if_result<_InIter, _OutIter>
     operator()(_InIter __first, _Sent __last, _OutIter __result, _Pred __pred, _Proj __proj = {}) const {
-    // TODO: implement
-    (void)__first; (void)__last; (void)__result; (void)__pred; (void)__proj;
-    return {};
+      return ranges::__remove_copy_if_impl(std::move(__first), std::move(__last), std::move(__result), __pred, __proj);
     }
 
-  template <input_range _Range, weakly_incrementable _OutIter, class _Proj = identity,
+    template <input_range _Range,
+              weakly_incrementable _OutIter,
+              class _Proj = identity,
               indirect_unary_predicate<projected<iterator_t<_Range>, _Proj>> _Pred>
       requires indirectly_copyable<iterator_t<_Range>, _OutIter>
-  _LIBCPP_HIDE_FROM_ABI constexpr
-  remove_copy_if_result<borrowed_iterator_t<_Range>, _OutIter>
+    _LIBCPP_HIDE_FROM_ABI constexpr remove_copy_if_result<borrowed_iterator_t<_Range>, _OutIter>
     operator()(_Range&& __range, _OutIter __result, _Pred __pred, _Proj __proj = {}) const {
-    // TODO: implement
-    (void)__range; (void)__result; (void)__pred; (void)__proj;
-    return {};
+      return ranges::__remove_copy_if_impl(
+          ranges::begin(__range), ranges::end(__range), std::move(__result), __pred, __proj);
     }
-
   };
 
 } // namespace __remove_copy_if
 
 inline namespace __cpo {
   inline constexpr auto remove_copy_if = __remove_copy_if::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
 
 #endif // _LIBCPP___ALGORITHM_RANGES_REMOVE_COPY_IF_H

libcxx/include/algorithm

template<input_range R1, input_range R2, class Pred = ranges::equal_to,
   template<input_iterator I1, sentinel_for<I1> S1, input_iterator I2, sentinel_for<I2> S2,
            weakly_incrementable O, class Comp = ranges::less,
            class Proj1 = identity, class Proj2 = identity>
     requires mergeable<I1, I2, O, Comp, Proj1, Proj2>
     constexpr set_symmetric_difference_result<I1, I2, O>
       set_symmetric_difference(I1 first1, S1 last1, I2 first2, S2 last2, O result,
                                Comp comp = {}, Proj1 proj1 = {},
                                Proj2 proj2 = {});                                                   // since C++20
-  
   template<input_range R1, input_range R2, weakly_incrementable O,
            class Comp = ranges::less, class Proj1 = identity, class Proj2 = identity>
     requires mergeable<iterator_t<R1>, iterator_t<R2>, O, Comp, Proj1, Proj2>
     constexpr set_symmetric_difference_result<borrowed_iterator_t<R1>,
                                                       borrowed_iterator_t<R2>, O>
       set_symmetric_difference(R1&& r1, R2&& r2, O result, Comp comp = {},
                                Proj1 proj1 = {}, Proj2 proj2 = {});                                 // since C++20
 
   template<forward_iterator I, sentinel_for<I> S, class T, class Proj = identity,
            indirect_strict_weak_order<const T*, projected<I, Proj>> Comp = ranges::less>
     constexpr subrange<I>
       equal_range(I first, S last, const T& value, Comp comp = {}, Proj proj = {});                 // since C++20
-  
   template<forward_range R, class T, class Proj = identity,
            indirect_strict_weak_order<const T*, projected<iterator_t<R>, Proj>> Comp =
              ranges::less>
     constexpr borrowed_subrange_t<R>
       equal_range(R&& r, const T& value, Comp comp = {}, Proj proj = {});                           // since C++20
-  
   template<class I1, class I2, class O>
     using set_union_result = in_in_out_result<I1, I2, O>;                                           // since C++20
 
   template<input_iterator I1, sentinel_for<I1> S1, input_iterator I2, sentinel_for<I2> S2,
            weakly_incrementable O, class Comp = ranges::less,
            class Proj1 = identity, class Proj2 = identity>
     requires mergeable<I1, I2, O, Comp, Proj1, Proj2>
     constexpr set_union_result<I1, I2, O>
       set_union(I1 first1, S1 last1, I2 first2, S2 last2, O result, Comp comp = {},
                 Proj1 proj1 = {}, Proj2 proj2 = {});                                                // since C++20
 
   template<input_range R1, input_range R2, weakly_incrementable O,
            class Comp = ranges::less, class Proj1 = identity, class Proj2 = identity>
     requires mergeable<iterator_t<R1>, iterator_t<R2>, O, Comp, Proj1, Proj2>
     constexpr set_union_result<borrowed_iterator_t<R1>, borrowed_iterator_t<R2>, O>
       set_union(R1&& r1, R2&& r2, O result, Comp comp = {},
                 Proj1 proj1 = {}, Proj2 proj2 = {});                                                // since C++20
 
   template<input_iterator I1, sentinel_for<I1> S1, input_iterator I2, sentinel_for<I2> S2,
            class Proj1 = identity, class Proj2 = identity,
            indirect_strict_weak_order<projected<I1, Proj1>, projected<I2, Proj2>> Comp =
              ranges::less>
     constexpr bool includes(I1 first1, S1 last1, I2 first2, S2 last2, Comp comp = {},
                             Proj1 proj1 = {}, Proj2 proj2 = {});                                   // Since C++20
-  
   template<input_range R1, input_range R2, class Proj1 = identity,
            class Proj2 = identity,
            indirect_strict_weak_order<projected<iterator_t<R1>, Proj1>,
                                       projected<iterator_t<R2>, Proj2>> Comp = ranges::less>
     constexpr bool includes(R1&& r1, R2&& r2, Comp comp = {},
                             Proj1 proj1 = {}, Proj2 proj2 = {});                                   // Since C++20
+
+  template<input_iterator I, sentinel_for<I> S, weakly_incrementable O, class T,
+           class Proj = identity>
+             indirect_binary_predicate<ranges::equal_to, projected<I, Proj>, const T*>
+    constexpr remove_copy_result<I, O>
+      remove_copy(I first, S last, O result, const T& value, Proj proj = {});                      // Since C++20
+
+  template<input_range R, weakly_incrementable O, class T, class Proj = identity>
+    requires indirectly_copyable<iterator_t<R>, O> &&
+             indirect_binary_predicate<ranges::equal_to,
+                                       projected<iterator_t<R>, Proj>, const T*>
+    constexpr remove_copy_result<borrowed_iterator_t<R>, O>
+      remove_copy(R&& r, O result, const T& value, Proj proj = {});                                // Since C++20
+
+  template<input_iterator I, sentinel_for<I> S, weakly_incrementable O,
+           class Proj = identity, indirect_unary_predicate<projected<I, Proj>> Pred>
+    requires indirectly_copyable<I, O>
+    constexpr remove_copy_if_result<I, O>
+      remove_copy_if(I first, S last, O result, Pred pred, Proj proj = {});                        // Since C++20
+
+  template<input_range R, weakly_incrementable O, class Proj = identity,
+           indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred>
+    requires indirectly_copyable<iterator_t<R>, O>
+    constexpr remove_copy_if_result<borrowed_iterator_t<R>, O>
+      remove_copy_if(R&& r, O result, Pred pred, Proj proj = {});                                  // Since C++20
+
 }
 
     constexpr bool     // constexpr in C++20
     all_of(InputIterator first, InputIterator last, Predicate pred);
 
 template <class InputIterator, class Predicate>
     constexpr bool     // constexpr in C++20
     any_of(InputIterator first, InputIterator last, Predicate pred);

 #include <__algorithm/ranges_nth_element.h>
 #include <__algorithm/ranges_partial_sort.h>
 #include <__algorithm/ranges_partition.h>
 #include <__algorithm/ranges_partition_copy.h>
 #include <__algorithm/ranges_partition_point.h>
 #include <__algorithm/ranges_pop_heap.h>
 #include <__algorithm/ranges_push_heap.h>
 #include <__algorithm/ranges_remove.h>
+#include <__algorithm/ranges_remove_copy.h>
+#include <__algorithm/ranges_remove_copy_if.h>
 #include <__algorithm/ranges_remove_if.h>
 #include <__algorithm/ranges_replace.h>
 #include <__algorithm/ranges_replace_if.h>
 #include <__algorithm/ranges_reverse.h>
 #include <__algorithm/ranges_reverse_copy.h>
 #include <__algorithm/ranges_rotate_copy.h>
 #include <__algorithm/ranges_search.h>
 #include <__algorithm/ranges_search_n.h>

libcxx/test/libcxx/algorithms/ranges_robust_against_copying_comparators.pass.cpp

#endif
     (void)std::ranges::partition_point(first, last, UnaryTrue(&copies)); assert(copies == 0);
     (void)std::ranges::partition_point(a, UnaryTrue(&copies)); assert(copies == 0);
     (void)std::ranges::pop_heap(first, last, Less(&copies)); assert(copies == 0);
     (void)std::ranges::pop_heap(a, Less(&copies)); assert(copies == 0);
     //(void)std::ranges::prev_permutation(first, last, Less(&copies)); assert(copies == 0);
     //(void)std::ranges::prev_permutation(a, Less(&copies)); assert(copies == 0);
     (void)std::ranges::push_heap(first, last, Less(&copies)); assert(copies == 0);
     (void)std::ranges::push_heap(a, Less(&copies)); assert(copies == 0);
-    //(void)std::ranges::remove_copy_if(first, last, first2, UnaryTrue(&copies)); assert(copies == 0);
-    //(void)std::ranges::remove_copy_if(a, first2, UnaryTrue(&copies)); assert(copies == 0);
+    (void)std::ranges::remove_copy_if(first, last, first2, UnaryTrue(&copies)); assert(copies == 0);
+    (void)std::ranges::remove_copy_if(a, first2, UnaryTrue(&copies)); assert(copies == 0);
     (void)std::ranges::remove_if(first, last, UnaryTrue(&copies)); assert(copies == 0);
     (void)std::ranges::remove_if(a, UnaryTrue(&copies)); assert(copies == 0);
     //(void)std::ranges::replace_copy_if(first, last, first2, UnaryTrue(&copies), value); assert(copies == 0);
     //(void)std::ranges::replace_copy_if(a, first2, UnaryTrue(&copies), value); assert(copies == 0);
     (void)std::ranges::replace_if(first, last, UnaryTrue(&copies), value); assert(copies == 0);
     (void)std::ranges::replace_if(a, UnaryTrue(&copies), value); assert(copies == 0);
     (void)std::ranges::search(first, last, first2, mid2, Equal(&copies)); assert(copies == 0);
     (void)std::ranges::search(a, b, Equal(&copies)); assert(copies == 0);

libcxx/test/libcxx/algorithms/ranges_robust_against_copying_projections.pass.cpp

#endif
     (void)std::ranges::partition_point(first, last, UnaryTrue(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::partition_point(a, UnaryTrue(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::pop_heap(first, last, Less(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::pop_heap(a, Less(), Proj(&copies)); assert(copies == 0);
     //(void)std::ranges::prev_permutation(first, last, Less(), Proj(&copies)); assert(copies == 0);
     //(void)std::ranges::prev_permutation(a, Less(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::push_heap(first, last, Less(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::push_heap(a, Less(), Proj(&copies)); assert(copies == 0);
-    //(void)std::ranges::remove_copy(first, last, first2, value, Proj(&copies)); assert(copies == 0);
-    //(void)std::ranges::remove_copy(a, first2, value, Proj(&copies)); assert(copies == 0);
-    //(void)std::ranges::remove_copy_if(first, last, first2, UnaryTrue(), Proj(&copies)); assert(copies == 0);
-    //(void)std::ranges::remove_copy_if(a, first2, UnaryTrue(), Proj(&copies)); assert(copies == 0);
+    (void)std::ranges::remove_copy(first, last, first2, value, Proj(&copies)); assert(copies == 0);
+    (void)std::ranges::remove_copy(a, first2, value, Proj(&copies)); assert(copies == 0);
+    (void)std::ranges::remove_copy_if(first, last, first2, UnaryTrue(), Proj(&copies)); assert(copies == 0);
+    (void)std::ranges::remove_copy_if(a, first2, UnaryTrue(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::remove(first, last, value, Proj(&copies)); assert(copies == 0);
     (void)std::ranges::remove(a, value, Proj(&copies)); assert(copies == 0);
     (void)std::ranges::remove_if(first, last, UnaryTrue(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::remove_if(a, UnaryTrue(), Proj(&copies)); assert(copies == 0);
     //(void)std::ranges::replace_copy(first, last, first2, value, T(), Proj(&copies)); assert(copies == 0);
     //(void)std::ranges::replace_copy(a, first2, value, T(), Proj(&copies)); assert(copies == 0);
     //(void)std::ranges::replace_copy_if(first, last, first2, UnaryTrue(), T(), Proj(&copies)); assert(copies == 0);
     //(void)std::ranges::replace_copy_if(a, first2, UnaryTrue(), T(), Proj(&copies)); assert(copies == 0);

libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/ranges_remove_copy.pass.cpp

 
 #include <algorithm>
 #include <array>
 #include <concepts>
 #include <functional>
 #include <ranges>
 
 #include "almost_satisfies_types.h"
+#include "counting_projection.h"
 #include "test_iterators.h"
 
-// TODO: SFINAE tests.
+template <class Iter, class Sent = sentinel_wrapper<Iter>, class OutIter = int*>
+concept HasRemoveCopyIt =
+    requires(Iter first, Sent last, OutIter result) { std::ranges::remove_copy(first, last, result, 0); };
+
+static_assert(HasRemoveCopyIt<int*>);
+static_assert(!HasRemoveCopyIt<InputIteratorNotDerivedFrom>);
+static_assert(!HasRemoveCopyIt<InputIteratorNotIndirectlyReadable>);
+static_assert(!HasRemoveCopyIt<InputIteratorNotInputOrOutputIterator>);
+static_assert(!HasRemoveCopyIt<int*, SentinelForNotSemiregular>);
+static_assert(!HasRemoveCopyIt<int*, SentinelForNotWeaklyEqualityComparableWith>);
+static_assert(!HasRemoveCopyIt<int*, int*, OutputIteratorNotIndirectlyWritable>);
+static_assert(!HasRemoveCopyIt<int*, int*, OutputIteratorNotInputOrOutputIterator>);
+
+template <class Range, class OutIter = int*>
+concept HasRemoveCopyR = requires(Range range, OutIter result) { std::ranges::remove_copy(range, result, 0); };
+
+static_assert(HasRemoveCopyR<UncheckedRange<int*>>);
+static_assert(!HasRemoveCopyR<InputRangeNotDerivedFrom>);
+static_assert(!HasRemoveCopyR<InputRangeNotIndirectlyReadable>);
+static_assert(!HasRemoveCopyR<InputRangeNotInputOrOutputIterator>);
+static_assert(!HasRemoveCopyR<InputRangeNotSentinelSemiregular>);
+static_assert(!HasRemoveCopyR<InputRangeNotSentinelEqualityComparableWith>);
+static_assert(!HasRemoveCopyR<UncheckedRange<int*>, OutputIteratorNotIndirectlyWritable>);
+static_assert(!HasRemoveCopyR<UncheckedRange<int*>, OutputIteratorNotInputOrOutputIterator>);
+
+template <int N, int M>
+struct Data {
+  std::array<int, N> input;
+  std::array<int, M> expected;
+  int val;
+};
+
+template <class InIter, class Sent, class OutIter, int N, int M>
+constexpr void test(Data<N, M> d) {
+  { // iterator overload
+    std::array<int, M> output;
+
+    std::same_as<std::ranges::in_out_result<InIter, OutIter>> decltype(auto) ret = std::ranges::remove_copy(
+        InIter(d.input.data()), Sent(InIter(d.input.data() + d.input.size())), OutIter(output.data()), d.val);
+
+    assert(base(ret.in) == d.input.data() + N);
+    assert(base(ret.out) == output.data() + M);
+    assert(d.expected == output);
+  }
+
+  { // range overload
+    std::array<int, M> output;
+    auto range = std::ranges::subrange(InIter(d.input.data()), Sent(InIter(d.input.data() + d.input.size())));
+
+    std::same_as<std::ranges::in_out_result<InIter, OutIter>> decltype(auto) ret =
+        std::ranges::remove_copy(range, OutIter(output.data()), d.val);
+
+    assert(base(ret.in) == d.input.data() + N);
+    assert(base(ret.out) == output.data() + M);
+    assert(d.expected == output);
+  }
+}
+
+template <class Iter, class Sent, class OutIter>
+constexpr void tests() {
+  // simple test
+  test<Iter, Sent, OutIter, 6, 5>({.input = {1, 2, 3, 4, 5, 6}, .expected = {1, 2, 3, 4, 6}, .val = 5});
+  // empty range
+  test<Iter, Sent, OutIter, 0, 0>({});
+  // single element range - match
+  test<Iter, Sent, OutIter, 1, 0>({.input = {1}, .expected = {}, .val = 1});
+  // single element range - no match
+  test<Iter, Sent, OutIter, 1, 1>({.input = {1}, .expected = {1}, .val = 2});
+  // two element range - same order
+  test<Iter, Sent, OutIter, 2, 1>({.input = {1, 2}, .expected = {1}, .val = 2});
+  // two element range - reversed order
+  test<Iter, Sent, OutIter, 2, 1>({.input = {1, 2}, .expected = {2}, .val = 1});
+  // all elements match
+  test<Iter, Sent, OutIter, 5, 0>({.input = {1, 1, 1, 1, 1}, .expected = {}, .val = 1});
+  // the relative order of elements isn't changed
+  test<Iter, Sent, OutIter, 8, 5>({.input = {1, 2, 3, 2, 3, 4, 2, 5}, .expected = {1, 3, 3, 4, 5}, .val = 2});
+}
+
+template <class InIter, class Sent>
+constexpr void test_output_iterators() {
+  tests<InIter, Sent, cpp17_output_iterator<int*>>();
+  tests<InIter, Sent, forward_iterator<int*>>();
+  tests<InIter, Sent, bidirectional_iterator<int*>>();
+  tests<InIter, Sent, random_access_iterator<int*>>();
+  tests<InIter, Sent, contiguous_iterator<int*>>();
+  tests<InIter, Sent, int*>();
+}
+
+template <class Iter>
+constexpr void test_sentinels() {
+  test_output_iterators<Iter, Iter>();
+  test_output_iterators<Iter, sentinel_wrapper<Iter>>();
+  test_output_iterators<Iter, sized_sentinel<Iter>>();
+}
 
 constexpr bool test() {
-  // TODO: main tests.
-  // TODO: A custom comparator works.
-  // TODO: A custom projection works.
+  test_output_iterators<cpp17_input_iterator<int*>, sentinel_wrapper<cpp17_input_iterator<int*>>>();
+  test_output_iterators<cpp17_input_iterator<int*>, sized_sentinel<cpp17_input_iterator<int*>>>();
+  test_output_iterators<cpp20_input_iterator<int*>, sentinel_wrapper<cpp20_input_iterator<int*>>>();
+  test_output_iterators<cpp20_input_iterator<int*>, sized_sentinel<cpp20_input_iterator<int*>>>();
+  test_sentinels<forward_iterator<int*>>();
+  test_sentinels<bidirectional_iterator<int*>>();
+  test_sentinels<random_access_iterator<int*>>();
+  test_sentinels<contiguous_iterator<int*>>();
+  test_sentinels<int*>();
+
+  { // check that passing a different type works
+    struct S {
+      constexpr operator int() const { return 3; }
+    };
+    { // iterator overload
+      int a[] = {1, 2, 3, 4};
+      int b[3];
+      std::ranges::remove_copy(std::begin(a), std::end(a), std::begin(b), S{});
+    }
+    { // range overload
+      int a[] = {1, 2, 3, 4};
+      int b[3];
+      std::ranges::remove_copy(a, std::begin(b), S{});
+    }
+  }
+
+  { // check that a custom projection works
+    struct S {
+      constexpr operator int() const { return 3; }
+    };
+    { // iterator overload
+      int a[] = {1, 2, 3, 4};
+      int b[3];
+      std::ranges::remove_copy(std::begin(a), std::end(a), std::begin(b), S{});
+    }
+    { // range overload
+      int a[] = {1, 2, 3, 4};
+      int b[3];
+      std::ranges::remove_copy(a, std::begin(b), S{});
+    }
+  }
+
+  // Complexity: Exactly last - first applications of the corresponding predicate and any projection.
+
+  {
+    std::array in{4, 4, 5, 6};
+    std::array expected{5, 6};
+
+    // iterator overload
+    {
+      int numberOfProj = 0;
+      std::array<int, 2> out;
+      std::ranges::remove_copy(
+          in.begin(),
+          in.end(),
+          out.begin(),
+          4,
+          counting_projection(numberOfProj));
+
+      assert(numberOfProj == static_cast<int>(in.size()));
+
+      assert(std::ranges::equal(out, expected));
+    }
+
+    // range overload
+    {
+      int numberOfProj = 0;
+      std::array<int, 2> out;
+      std::ranges::remove_copy(
+          in, out.begin(), 4, counting_projection(numberOfProj));
+      assert(numberOfProj == static_cast<int>(in.size()));
+      assert(std::ranges::equal(out, expected));
+    }
+  }
 
   return true;
 }
 
 int main(int, char**) {
   test();
   static_assert(test());
 
   return 0;
 }

libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/ranges_remove_copy_if.pass.cpp

 //   constexpr remove_copy_if_result<borrowed_iterator_t<R>, O>
 //     remove_copy_if(R&& r, O result, Pred pred, Proj proj = {});                                  // Since C++20
 
 #include <algorithm>
 #include <array>
 #include <concepts>
 #include <functional>
 #include <ranges>
+#include <type_traits>
 
 #include "almost_satisfies_types.h"
+#include "counting_predicates.h"
+#include "counting_projection.h"
 #include "test_iterators.h"
 
-// TODO: SFINAE tests.
+struct AlwaysTrue {
+  constexpr bool operator()(auto&&...) const { return true; }
+};
+
+template <
+    class I,
+    class S    = sentinel_wrapper<std::decay_t<I>>,
+    class O    = int*,
+    class Pred = AlwaysTrue,
+    class Proj = std::identity>
+concept HasRemoveCopyIfIter =
+    requires(I&& iter, S&& sent, O&& out, Pred&& pred, Proj&& proj) {
+      std::ranges::remove_copy_if(
+          std::forward<I>(iter),
+          std::forward<S>(sent),
+          std::forward<O>(out),
+          std::forward<Pred>(pred),
+          std::forward<Proj>(proj));
+    };
+
+static_assert(HasRemoveCopyIfIter<int*, int*, int*>);
+
+// !input_iterator<I>
+static_assert(!HasRemoveCopyIfIter<InputIteratorNotDerivedFrom>);
+static_assert(!HasRemoveCopyIfIter<cpp20_output_iterator<int*>>);
+
+// !sentinel_for<S, I>
+static_assert(!HasRemoveCopyIfIter<int*, SentinelForNotWeaklyEqualityComparableWith>);
+static_assert(!HasRemoveCopyIfIter<int*, SentinelForNotSemiregular>);
+
+// !weakly_incrementable<O>
+static_assert(!HasRemoveCopyIfIter<int*, int*, WeaklyIncrementableNotMovable>);
+
+// !indirect_unary_predicate<Pred, projected<I, Proj>>
+static_assert(!HasRemoveCopyIfIter<int*, int*, int*, IndirectUnaryPredicateNotPredicate>);
+static_assert(!HasRemoveCopyIfIter<int*, int*, int*, IndirectUnaryPredicateNotCopyConstructible>);
+
+// !indirectly_copyable<I, O>
+static_assert(!HasRemoveCopyIfIter<int*, int*, OutputIteratorNotIndirectlyWritable>);
+static_assert(!HasRemoveCopyIfIter<const int*, const int*, const int*>);
+
+template < class R, class O = int*, class Pred = AlwaysTrue, class Proj = std::identity>
+concept HasRemoveCopyIfRange =
+    requires(R&& r, O&& out, Pred&& pred, Proj&& proj) {
+      std::ranges::remove_copy_if(
+          std::forward<R>(r), std::forward<O>(out), std::forward<Pred>(pred), std::forward<Proj>(proj));
+    };
+
+template <class T>
+using R = UncheckedRange<T>;
+
+static_assert(HasRemoveCopyIfRange<R<int*>>);
+
+// !input_range<R>
+static_assert(!HasRemoveCopyIfRange<R<InputIteratorNotDerivedFrom>>);
+static_assert(!HasRemoveCopyIfRange<R<cpp20_output_iterator<int*>>>);
+
+// !weakly_incrementable<O>
+static_assert(!HasRemoveCopyIfRange<R<int*>, WeaklyIncrementableNotMovable>);
+
+// !indirect_unary_predicate<Pred, projected<iterator_t<R>, Proj>>
+static_assert(!HasRemoveCopyIfRange<R<int*>, int*, IndirectUnaryPredicateNotPredicate>);
+static_assert(!HasRemoveCopyIfRange<R<int*>, int*, IndirectUnaryPredicateNotCopyConstructible>);
+
+// !indirectly_copyable<iterator_t<R>, O>
+static_assert(!HasRemoveCopyIfRange<R<int*>, OutputIteratorNotIndirectlyWritable>);
+static_assert(!HasRemoveCopyIfRange<R<const int*>, const int*>);
+
+template <class InIter, class OutIter, template <class> class SentWrapper, std::size_t N1, std::size_t N2, class Pred>
+constexpr void testRemoveCopyIfImpl(std::array<int, N1> in, std::array<int, N2> expected, Pred pred) {
+  using Sent = SentWrapper<InIter>;
+
+  // iterator overload
+  {
+    std::array<int, N2> out;
+    std::same_as<std::ranges::remove_copy_if_result<InIter, OutIter>> decltype(auto) result =
+        std::ranges::remove_copy_if(InIter{in.data()}, Sent{InIter{in.data() + in.size()}}, OutIter{out.data()}, pred);
+    assert(std::ranges::equal(out, expected));
+    assert(base(result.in) == in.data() + in.size());
+    assert(base(result.out) == out.data() + out.size());
+  }
+
+  // range overload
+  {
+    std::array<int, N2> out;
+    std::ranges::subrange r{InIter{in.data()}, Sent{InIter{in.data() + in.size()}}};
+    std::same_as<std::ranges::remove_copy_if_result<InIter, OutIter>> decltype(auto) result =
+        std::ranges::remove_copy_if(r, OutIter{out.data()}, pred);
+    assert(std::ranges::equal(out, expected));
+    assert(base(result.in) == in.data() + in.size());
+    assert(base(result.out) == out.data() + out.size());
+  }
+}
+
+template <class InIter, class OutIter, template <class> class SentWrapper>
+constexpr void testImpl() {
+  // remove multiple elements
+  {
+    std::array in{1, 2, 3, 2, 1};
+    std::array expected{1, 3, 1};
+    auto pred = [](int i) { return i == 2; };
+    testRemoveCopyIfImpl<InIter, OutIter, SentWrapper>(in, expected, pred);
+  }
+
+  // remove single elements
+  {
+    std::array in{1, 2, 3, 2, 1};
+    std::array expected{1, 2, 2, 1};
+    auto pred = [](int i) { return i == 3; };
+    testRemoveCopyIfImpl<InIter, OutIter, SentWrapper>(in, expected, pred);
+  }
+
+  // nothing removed
+  {
+    std::array in{1, 2, 3, 2, 1};
+    std::array expected{1, 2, 3, 2, 1};
+    auto pred = [](int) { return false; };
+    testRemoveCopyIfImpl<InIter, OutIter, SentWrapper>(in, expected, pred);
+  }
+
+  // all removed
+  {
+    std::array in{1, 2, 3, 2, 1};
+    std::array<int, 0> expected{};
+    auto pred = [](int) { return true; };
+    testRemoveCopyIfImpl<InIter, OutIter, SentWrapper>(in, expected, pred);
+  }
+
+  // remove first
+  {
+    std::array in{1, 2, 3, 2};
+    std::array expected{2, 3, 2};
+    auto pred = [](int i) { return i < 2; };
+    testRemoveCopyIfImpl<InIter, OutIter, SentWrapper>(in, expected, pred);
+  }
+
+  // remove last
+  {
+    std::array in{1, 2, 3, 2, 5};
+    std::array expected{1, 2, 3, 2};
+    auto pred = [](int i) { return i > 3; };
+    testRemoveCopyIfImpl<InIter, OutIter, SentWrapper>(in, expected, pred);
+  }
+
+  // stable
+  {
+    std::array in{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
+    std::array expected{6, 7, 8, 9, 10};
+    auto pred = [](int i) { return i < 6; };
+    testRemoveCopyIfImpl<InIter, OutIter, SentWrapper>(in, expected, pred);
+  }
+
+  // empty range
+  {
+    std::array<int, 0> in{};
+    std::array<int, 0> expected{};
+    auto pred = [](int) { return false; };
+    testRemoveCopyIfImpl<InIter, OutIter, SentWrapper>(in, expected, pred);
+  }
+
+  // one element range
+  {
+    std::array in{1};
+    std::array<int, 0> expected{};
+    auto pred = [](int i) { return i == 1; };
+    testRemoveCopyIfImpl<InIter, OutIter, SentWrapper>(in, expected, pred);
+  }
+}
+
+template <class OutIter, template <class> class SentWrapper>
+constexpr void withAllPermutationsOfInIter() {
+  testImpl<cpp20_input_iterator<int*>, OutIter, sentinel_wrapper>();
+  testImpl<forward_iterator<int*>, OutIter, SentWrapper>();
+  testImpl<bidirectional_iterator<int*>, OutIter, SentWrapper>();
+  testImpl<random_access_iterator<int*>, OutIter, SentWrapper>();
+  testImpl<contiguous_iterator<int*>, OutIter, SentWrapper>();
+  testImpl<int*, OutIter, SentWrapper>();
+}
+
+template <template <class> class SentWrapper>
+constexpr void withAllPermutationsOfInIterOutIter() {
+  withAllPermutationsOfInIter<cpp20_output_iterator<int*>, SentWrapper>();
+  withAllPermutationsOfInIter<int*, SentWrapper>();
+}
 
 constexpr bool test() {
-  // TODO: main tests.
-  // TODO: A custom comparator works.
-  // TODO: A custom projection works.
+  withAllPermutationsOfInIterOutIter<std::type_identity_t>();
+  withAllPermutationsOfInIterOutIter<sentinel_wrapper>();
+
+  // Test custom projection
+  {
+    struct Data {
+      int data;
+    };
+
+    std::array in{Data{4}, Data{8}, Data{12}, Data{12}};
+    std::array expected{Data{4}, Data{12}, Data{12}};
+
+    const auto proj = &Data::data;
+    const auto pred = [](int i) { return i == 8; };
+
+    const auto equals = [](const Data& x, const Data& y) { return x.data == y.data; };
+    // iterator overload
+    {
+      std::array<Data, 3> out;
+      auto result = std::ranges::remove_copy_if(in.begin(), in.end(), out.begin(), pred, proj);
+      assert(std::ranges::equal(out, expected, equals));
+      assert(result.in == in.end());
+      assert(result.out == out.end());
+    }
+
+    // range overload
+    {
+      std::array<Data, 3> out;
+      auto result = std::ranges::remove_copy_if(in, out.begin(), pred, proj);
+      assert(std::ranges::equal(out, expected, equals));
+      assert(result.in == in.end());
+      assert(result.out == out.end());
+    }
+  }
+
+  // Complexity: Exactly last - first applications of the corresponding predicate and any projection.
+  {
+    std::array in{4, 4, 5, 6};
+    std::array expected{5, 6};
+
+    const auto pred = [](int i) { return i == 4; };
+
+    // iterator overload
+    {
+      int numberOfPred = 0;
+      int numberOfProj = 0;
+      std::array<int, 2> out;
+      std::ranges::remove_copy_if(
+          in.begin(), in.end(), out.begin(), counting_predicate(pred, numberOfPred), counting_projection(numberOfProj));
+
+      assert(numberOfPred == static_cast<int>(in.size()));
+      assert(numberOfProj == static_cast<int>(in.size()));
+
+      assert(std::ranges::equal(out, expected));
+    }
+
+    // range overload
+    {
+      int numberOfPred = 0;
+      int numberOfProj = 0;
+      std::array<int, 2> out;
+      std::ranges::remove_copy_if(
+          in, out.begin(), counting_predicate(pred, numberOfPred), counting_projection(numberOfProj));
+      assert(numberOfPred == static_cast<int>(in.size()));
+      assert(numberOfProj == static_cast<int>(in.size()));
+      assert(std::ranges::equal(out, expected));
+    }
+  }
 
   return true;
 }
 
 int main(int, char**) {
   test();
   static_assert(test());
 
   return 0;
 }

libcxx/test/std/algorithms/ranges_result_alias_declarations.compile.pass.cpp

 
 static_assert(std::is_same_v<in_out_result<int, long>, copy_result<int, long>>);
 static_assert(std::is_same_v<in_out_result<int, long>, copy_n_result<int, long>>);
 static_assert(std::is_same_v<in_out_result<int, long>, copy_if_result<int, long>>);
 static_assert(std::is_same_v<in_out_result<int, long>, copy_backward_result<int, long>>);
 static_assert(std::is_same_v<in_out_result<int, long>, move_result<int, long>>);
 static_assert(std::is_same_v<in_out_result<int, long>, move_backward_result<int, long>>);
 // static_assert(std::is_same_v<in_out_result<int, long>, partial_sort_copy_result<int, long>>);
-// static_assert(std::is_same_v<in_out_result<int, long>, remove_copy_result<int, long>>);
-// static_assert(std::is_same_v<in_out_result<int, long>, remove_copy_if_result<int, long>>);
+static_assert(std::is_same_v<in_out_result<int, long>, remove_copy_result<int, long>>);
+static_assert(std::is_same_v<in_out_result<int, long>, remove_copy_if_result<int, long>>);
 // static_assert(std::is_same_v<in_out_result<int, long>, replace_copy_result<int, long>>);
 // static_assert(std::is_same_v<in_out_result<int, long>, replace_copy_if_result<int, long>>);
 // static_assert(std::is_same_v<in_out_result<int, long>, reverse_copy_result<int, long>>);
 // static_assert(std::is_same_v<in_out_result<int, long>, rotate_copy_result<int, long>>);
 static_assert(std::is_same_v<in_out_result<int, long>, set_difference_result<int, long>>);
 static_assert(std::is_same_v<in_out_result<int, long>, unary_transform_result<int, long>>);
 static_assert(std::is_same_v<in_out_result<int, long>, uninitialized_copy_result<int, long>>);
 static_assert(std::is_same_v<in_out_result<int, long>, uninitialized_copy_n_result<int, long>>);

libcxx/test/std/algorithms/ranges_robust_against_dangling.pass.cpp

constexpr bool test_all() {
   using std::ranges::for_each_result;
   using std::ranges::merge_result;
   using std::ranges::minmax_result;
   using std::ranges::mismatch_result;
   using std::ranges::move_result;
   //using std::ranges::move_backward_result;
   //using std::ranges::partial_sort_copy_result;
   using std::ranges::partition_copy_result;
-  //using std::ranges::remove_copy_result;
-  //using std::ranges::remove_copy_if_result;
+  using std::ranges::remove_copy_result;
+  using std::ranges::remove_copy_if_result;
   using std::ranges::reverse_copy_result;
   using std::ranges::rotate_copy_result;
   using std::ranges::set_difference_result;
   using std::ranges::set_intersection_result;
   using std::ranges::set_symmetric_difference_result;
   using std::ranges::set_union_result;
   using std::ranges::swap_ranges_result;
   using std::ranges::unary_transform_result;
   //using std::ranges::unique_copy_result;
 
   auto unary_pred = [](int i) { return i > 0; };
   auto binary_pred = [](int i, int j) { return i < j; };
   //auto gen = [] { return 42; };
 
   std::array in = {1, 2, 3};
   std::array in2 = {4, 5, 6};
 
dangling_1st(std::ranges::fill, in, x);
     dangling_1st<binary_transform_result<dangling, int*, bool*>>(
         std::ranges::transform, in, in2, out_transform.begin(), binary_pred);
     dangling_2nd<binary_transform_result<int*, dangling, bool*>>(
         std::ranges::transform, in, in2, out_transform.begin(), binary_pred);
     dangling_both<binary_transform_result<dangling, dangling, bool*>>(
         std::ranges::transform, in, in2, out_transform.begin(), binary_pred);
   }
   //dangling_1st(std::ranges::generate, in, gen);
-  //dangling_1st<remove_copy_result<dangling, int*>>(std::ranges::remove_copy, in, out, x);
-  //dangling_1st<remove_copy_if_result<dangling, int*>>(std::ranges::remove_copy_if, in, out, unary_pred);
+  dangling_1st<remove_copy_result<dangling, int*>>(std::ranges::remove_copy, in, out, x);
+  dangling_1st<remove_copy_if_result<dangling, int*>>(std::ranges::remove_copy_if, in, out, unary_pred);
   dangling_1st(std::ranges::replace, in, x, x);
   dangling_1st(std::ranges::replace_if, in, std::identity{}, x);
   //dangling_1st(std::ranges::replace_copy, in, out, x, x);
   //dangling_1st(std::ranges::replace_copy_if, in, out, x, x);
   dangling_1st<swap_ranges_result<dangling, int*>>(std::ranges::swap_ranges, in, in2);
   dangling_2nd<swap_ranges_result<int*, dangling>>(std::ranges::swap_ranges, in, in2);
   dangling_both<swap_ranges_result<dangling, dangling>>(std::ranges::swap_ranges, in, in2);
   dangling_1st<reverse_copy_result<dangling, int*>>(std::ranges::reverse_copy, in, out);

libcxx/test/std/algorithms/ranges_robust_against_nonbool_predicates.pass.cpp

constexpr bool test_all() {
   test(std::ranges::is_sorted, in, binary_pred);
   test(std::ranges::is_sorted_until, in, binary_pred);
   test(std::ranges::includes, in, in2, binary_pred);
   //test(std::ranges::is_heap, in, binary_pred);
   //test(std::ranges::is_heap_until, in, binary_pred);
   //std::ranges::clamp(2, 1, 3, binary_pred);
   //test(std::ranges::is_permutation, in, in2, binary_pred);
   test(std::ranges::copy_if, in, out, unary_pred);
-  //test(std::ranges::remove_copy_if, in, out, unary_pred);
+  test(std::ranges::remove_copy_if, in, out, unary_pred);
   test(std::ranges::replace_if, in, unary_pred, x);
   //test(std::ranges::replace_copy_if, in, out, unary_pred, x);
   //test(std::ranges::unique_copy, in, out, binary_pred);
   test(std::ranges::partition_copy, in, out, out2, unary_pred);
   //test(std::ranges::partial_sort_copy, in, in2, binary_pred);
   test(std::ranges::merge, in, in2, out, binary_pred);
   test(std::ranges::set_difference, in, in2, out, binary_pred);
   test(std::ranges::set_intersection, in, in2, out, binary_pred);

libcxx/test/std/algorithms/ranges_robust_against_omitting_invoke.pass.cpp

constexpr bool test_all() {
   // `move` and `move_backward` have neither a projection nor a predicate.
   // `fill` and `fill_n` have neither a projection nor a predicate.
   {
     std::array out_transform = {false, true, true};
     test(std::ranges::transform, in, out_transform.begin(), &Foo::unary_pred, &Bar::val);
   }
   //test(std::ranges::generate, in, &Bar::create);
   //std::ranges::generate_n(in.begin(), count, &Bar::create);
-  //test(std::ranges::remove_copy, in, out, x, &Bar::val);
-  //test(std::ranges::remove_copy_if, in, out, &Foo::unary_pred, &Bar::val);
+  test(std::ranges::remove_copy, in, out, x, &Bar::val);
+  test(std::ranges::remove_copy_if, in, out, &Foo::unary_pred, &Bar::val);
   // `replace*` algorithms only use the projection to compare the elements, not to write them.
   test(std::ranges::replace, in, x, a, &Bar::val);
   test(std::ranges::replace_if, in, &Foo::unary_pred, a, &Bar::val);
   //test(std::ranges::replace_copy, in, out, x, a, &Bar::val);
   //test(std::ranges::replace_copy_if, in, out, pred, a, &Bar::val);
   // `swap_ranges` has neither a projection nor a predicate.
   // `reverse_copy` has neither a projection nor a predicate.
   // `rotate_copy` has neither a projection nor a predicate.

libcxx/test/std/algorithms/ranges_robust_against_proxy_iterators.pass.cpp

if constexpr (std::copyable<T>) {
     test(std::ranges::fill, in, x);
     std::ranges::fill_n(in.begin(), count, x);
     test(std::ranges::transform, in, out, std::identity{});
     test(std::ranges::transform, in, in2, out, binary_func);
   }
   //test(std::ranges::generate, in, gen);
   //std::ranges::generate_n(in.begin(), count, gen);
   if constexpr (std::copyable<T>) {
-  //test(std::ranges::remove_copy, in, out, x);
-  //test(std::ranges::remove_copy_if, in, out, unary_pred);
+    test(std::ranges::remove_copy, in, out, x);
+    test(std::ranges::remove_copy_if, in, out, unary_pred);
     test(std::ranges::replace, in, x, x);
     test(std::ranges::replace_if, in, unary_pred, x);
     //test(std::ranges::replace_copy, in, out, x, x);
     //test(std::ranges::replace_copy_if, in, out, unary_pred, x);
   }
   test(std::ranges::swap_ranges, in, in2);
   if constexpr (std::copyable<T>) {
     test(std::ranges::reverse_copy, in, out);

libcxx/test/std/library/description/conventions/customization.point.object/niebloid.compile.pass.cpp

 //static_assert(test(std::ranges::partial_sort_copy, a, a));
 static_assert(test(std::ranges::partition, a, odd));
 static_assert(test(std::ranges::partition_copy, a, a, a, odd));
 static_assert(test(std::ranges::partition_point, a, odd));
 static_assert(test(std::ranges::pop_heap, a));
 //static_assert(test(std::ranges::prev_permutation, a));
 static_assert(test(std::ranges::push_heap, a));
 static_assert(test(std::ranges::remove, a, 42));
-//static_assert(test(std::ranges::remove_copy, a, a, 42));
-//static_assert(test(std::ranges::remove_copy_if, a, a, odd));
+static_assert(test(std::ranges::remove_copy, a, a, 42));
+static_assert(test(std::ranges::remove_copy_if, a, a, odd));
 static_assert(test(std::ranges::remove_if, a, odd));
 static_assert(test(std::ranges::replace, a, 42, 43));
 //static_assert(test(std::ranges::replace_copy, a, a, 42, 43));
 //static_assert(test(std::ranges::replace_copy_if, a, a, odd, 43));
 static_assert(test(std::ranges::replace_if, a, odd, 43));
 static_assert(test(std::ranges::reverse, a));
 static_assert(test(std::ranges::reverse_copy, a, a));
 //static_assert(test(std::ranges::rotate, a, a+5));

libcxx/test/support/counting_projection.h

 public:
   constexpr counting_projection() = default;
   constexpr counting_projection(int& count) : count_(&count) {}
   constexpr counting_projection(Proj proj, int& count) : proj_(std::move(proj)), count_(&count) {}
 
   template <class T>
   constexpr decltype(auto) operator()(T&& value) const {
     ++(*count_);
-    return proj_(std::forward<T>(value));
+    return std::invoke(proj_, std::forward<T>(value));
   }
 };
 
 counting_projection(int& count) -> counting_projection<std::identity>;
 template <class Proj>
 counting_projection(Proj proj, int& count) -> counting_projection<Proj>;
 
 #endif // TEST_STD_VER > 14
 
 #endif // TEST_SUPPORT_COUNTING_PROJECTION_H