[libcxx-commits] [PATCH] D102263: [libcxx][ranges] Fix `ranges::empty` when begin, end, and empty members are provided.

[Zoe Carver via Phabricator via libcxx-commits]

zoecarver created this revision.
zoecarver requested review of this revision.
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Herald added a reviewer: libc++.

Before this commit, we'd get a compilation error because the operator() overload was ambiguous.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D102263

Files:
  libcxx/include/__ranges/empty.h
  libcxx/test/std/ranges/range.access/range.prim/empty.pass.cpp


Index: libcxx/test/std/ranges/range.access/range.prim/empty.pass.cpp
===================================================================
--- libcxx/test/std/ranges/range.access/range.prim/empty.pass.cpp
+++ libcxx/test/std/ranges/range.access/range.prim/empty.pass.cpp
@@ -133,6 +133,13 @@
 inline constexpr bool std::disable_sized_range<DisabledSizeRangeWithBeginEnd> = true;
 static_assert(!std::is_invocable_v<RangeSizeT, DisabledSizeRangeWithBeginEnd&>);
 
+struct BeginEndAndEmpty {
+  int buff[8];
+  constexpr int* begin() { return buff; }
+  constexpr int* end() { return buff + 8; }
+  constexpr bool empty() { return true; }
+};
+
 constexpr bool testBeginEqualsEnd() {
   BeginEndNotSizedSentinel a;
   assert(std::ranges::empty(a) == true);
@@ -146,6 +153,9 @@
   DisabledSizeRangeWithBeginEnd d;
   assert(std::ranges::empty(d) == true);
 
+  BeginEndAndEmpty e;
+  assert(std::ranges::empty(e) == true);
+
   return true;
 }
 
Index: libcxx/include/__ranges/empty.h
===================================================================
--- libcxx/include/__ranges/empty.h
+++ libcxx/include/__ranges/empty.h
@@ -41,6 +41,7 @@
 
   template <class _Tp>
   concept __can_compare_begin_end =
+    !__member_empty<_Tp> &&
     !__can_invoke_size<_Tp> &&
     requires(_Tp&& __t) {
       bool(ranges::begin(__t) == ranges::end(__t));


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