[libcxx-commits] [libcxx] [libc++][ranges] implement `ranges::shift_left` (PR #83231)

[Xiaoyang Liu via libcxx-commits]

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@@ -0,0 +1,194 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// <algorithm>
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+
+// template<permutable I, sentinel_for<I> S>
+//   constexpr subrange<I> ranges::shift_left(I first, S last, iter_difference_t<I> n);
+
+// template<forward_range R>
+//   requires permutable<iterator_t<R>>
+//   constexpr borrowed_subrange_t<R> ranges::shift_left(R&& r, range_difference_t<R> n)
+
+#include <algorithm>
+#include <array>
+#include <ranges>
+#include <iterator>
+
+#include "almost_satisfies_types.h"
+#include "test_iterators.h"
+#include "MoveOnly.h"
+
+template <class Iter, class Sent = Iter, class Count = std::size_t>
+concept HasShiftLeftIt = requires(Iter iter, Sent sent, Count n) { std::ranges::shift_left(iter, sent, n); };
+
+static_assert(HasShiftLeftIt<int*>);
+static_assert(!HasShiftLeftIt<ForwardIteratorNotDerivedFrom>);
+static_assert(!HasShiftLeftIt<PermutableNotForwardIterator>);
+static_assert(!HasShiftLeftIt<PermutableNotSwappable>);
+
+template <class Range, class Count = std::size_t>
+concept HasShiftLeftR = requires(Range range, Count n) { std::ranges::shift_left(range, n); };
+
+static_assert(HasShiftLeftR<UncheckedRange<int*>>);
+static_assert(!HasShiftLeftR<ForwardRangeNotDerivedFrom>);
+static_assert(!HasShiftLeftR<PermutableRangeNotForwardIterator>);
+static_assert(!HasShiftLeftR<PermutableRangeNotSwappable>);
----------------
xiaoyang-sde wrote:

I'm not sure if these statements are sufficient. (I thought these tests are meant to check if the correctness of the constraints for `ranges::shift_left`. Correct me if I'm wrong.)


https://github.com/llvm/llvm-project/pull/83231