Write pmr memory resource 'counted_new_delete_resource'

test/helpers/pmr.hpp

@@ -0,0 +1,55 @@
+
+// Copyright 2024 Braden Ganetsky.
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or move at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_UNORDERED_TEST_PMR_HEADER
+#define BOOST_UNORDERED_TEST_PMR_HEADER
+
+#include <boost/config.hpp>
+
+#ifndef BOOST_NO_CXX17_HDR_MEMORY_RESOURCE
+
+#include <memory_resource>
+
+namespace test {
+  class counted_new_delete_resource : public std::pmr::memory_resource
+  {
+  public:
+    using std::pmr::memory_resource::memory_resource;
+    ~counted_new_delete_resource() override {}
+
+    std::size_t count() const { return _count; }
+
+  private:
+    void* do_allocate(std::size_t bytes, std::size_t alignment) override
+    {
+      _count += bytes;
+      return ::operator new(bytes, std::align_val_t(alignment));
+    }
+
+    void do_deallocate(
+      void* p, std::size_t bytes, std::size_t alignment) override
+    {
+      _count -= bytes;
+#if __cpp_sized_deallocation
+      ::operator delete(p, bytes, std::align_val_t(alignment));
+#else
+      ::operator delete(p, std::align_val_t(alignment));
+#endif
+    }
+
+    bool do_is_equal(
+      const std::pmr::memory_resource& other) const noexcept override
+    {
+      return this == &other;
+    }
+
+  private:
+    std::size_t _count = 0;
+  };
+} // namespace test
+
+#endif // !defined(BOOST_NO_CXX17_HDR_MEMORY_RESOURCE)
+
+#endif // !defined(BOOST_UNORDERED_TEST_PMR_HEADER)