[libc++][spaceship] P1614R2: Added `operator==` to `slice`

[H-G-Hristov]

Summary

Implements parts of P1614R2:

• Added operator== to slice

[H-G-Hristov]

Added synopsis

[Mordante]

Thanks for working on this! I would like to land D152297 first for this one too. But this needs some addition work.

libcxx/include/valarray

410

Note this function should be a hidden friend per http://eel.is/c++draft/hidden.friends.

libcxx/test/std/numerics/numarray/class.slice/slice.ops/slice.ops.pass.cpp

18

Why not use the normal test macros instead?

[H-G-Hristov]

Try to fix CI

[H-G-Hristov]

Addressed comments

[Mordante]

LGTM!

libcxx/include/valarray

 {
 public:
     slice();
     slice(size_t start, size_t size, size_t stride);
 
     size_t start()  const;
     size_t size()   const;
     size_t stride() const;
+
+    friend bool operator==(const slice& x, const slice& y); // since C++20
 };
 
 template <class T>
 class slice_array
 {
 public:
     typedef T value_type;
 
slice(size_t __start, size_t __size, size_t __stride)
         : __start_(__start),
           __size_(__size),
           __stride_(__stride)
           {}
 
     _LIBCPP_INLINE_VISIBILITY size_t start()  const {return __start_;}
     _LIBCPP_INLINE_VISIBILITY size_t size()   const {return __size_;}
     _LIBCPP_INLINE_VISIBILITY size_t stride() const {return __stride_;}
+
+#if _LIBCPP_STD_VER >= 20
+
+    friend bool operator==(const slice& __x, const slice& __y);
+
+#endif
 };
 
+#if _LIBCPP_STD_VER >= 20
+
+bool operator==(const slice& __x, const slice& __y)
+{
+  return __x.start() == __y.start() && __x.size() == __y.size() && __x.stride() == __y.stride();
+}
+
+#endif
+
+
 template <class _Tp> class _LIBCPP_TEMPLATE_VIS slice_array;
 class _LIBCPP_TYPE_VIS gslice;
 template <class _Tp> class _LIBCPP_TEMPLATE_VIS gslice_array;
 template <class _Tp> class _LIBCPP_TEMPLATE_VIS mask_array;
 template <class _Tp> class _LIBCPP_TEMPLATE_VIS indirect_array;
 
 template <class _Tp>
 _LIBCPP_INLINE_VISIBILITY

libcxx/test/std/numerics/numarray/class.slice/slice.ops/slice.ops.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// <valarray>
+
+// class slice;
+
+// friend bool operator==(const slice& x, const slice& y);
+
+#include <valarray>
+#include <cassert>
+
+int main(int, char**) {
+  {
+    std::slice s1;
+    std::slice s2;
+
+    assert(s1 == s2);
+    assert(s2 == s1);
+  }
+  {
+    std::slice s1(1, 2, 3);
+    std::slice s2{1, 2, 3};
+
+    assert(s1 == s2);
+    assert(s2 == s1);
+  }
+  {
+    std::slice s1(0, 2, 3);
+    std::slice s2{1, 2, 3};
+
+    assert(s1 != s2);
+    assert(s2 != s1);
+  }
+  {
+    std::slice s1(1, 0, 3);
+    std::slice s2{1, 2, 3};
+
+    assert(s1 != s2);
+    assert(s2 != s1);
+  }
+  {
+    std::slice s1(1, 2, 0);
+    std::slice s2{1, 2, 3};
+
+    assert(s1 != s2);
+    assert(s2 != s1);
+  }
+
+  return 0;
+}