Implement an _is_allocator type trait for use in deduction guides.
llvm-svn: 322306
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 0e22bf8cb963d34439c8aef38acf626c29f0f804
diff --git a/include/memory b/include/memory
index d6b427b..56502e2 100644
--- a/include/memory
+++ b/include/memory
@@ -5597,6 +5597,16 @@
};
#endif
+#if _LIBCPP_STD_VER > 14
+template<typename _Alloc, typename = void>
+struct __is_allocator : false_type {};
+
+template<typename _Alloc>
+struct __is_allocator<_Alloc,
+ void_t<typename _Alloc::value_type, decltype(_VSTD::declval<_Alloc&>().allocate(size_t{}))>>
+ : true_type {};
+#endif
+
_LIBCPP_END_NAMESPACE_STD
_LIBCPP_POP_MACROS
diff --git a/test/libcxx/memory/is_allocator.pass.cpp b/test/libcxx/memory/is_allocator.pass.cpp
new file mode 100644
index 0000000..c33b7e8
--- /dev/null
+++ b/test/libcxx/memory/is_allocator.pass.cpp
@@ -0,0 +1,41 @@
+//===----------------------------------------------------------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+
+// <memory>
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+// template<typename _Alloc>
+// struct __is_allocator;
+
+// Is either true_type or false_type depending on if A is an allocator.
+
+#include <memory>
+#include <string>
+
+#include "test_macros.h"
+#include "min_allocator.h"
+#include "test_allocator.h"
+
+template <typename T>
+void test_allocators()
+{
+ static_assert( std::__is_allocator<std::allocator<T>>::value, "" );
+ static_assert( std::__is_allocator<test_allocator<T>>::value, "" );
+ static_assert( std::__is_allocator<min_allocator<T>>::value, "" );
+}
+
+
+int main()
+{
+// test_allocators<void>();
+ test_allocators<char>();
+ test_allocators<int>();
+ test_allocators<std::string>();
+}