Get initial prototype of transparent count() working

test/unordered/transparent_tests.cpp

@@ -0,0 +1,64 @@
+// Copyright 2021 Christian Mazakas.
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+// clang-format off
+#include "../helpers/prefix.hpp"
+#include <boost/unordered_set.hpp>
+#include <boost/unordered_map.hpp>
+#include "../helpers/postfix.hpp"
+// clang-format on
+
+#include "../helpers/test.hpp"
+
+#include <boost/container_hash/hash.hpp>
+
+struct key {
+    int x_;
+    static int count_;
+
+    explicit key(int x) : x_(x) {
+        ++count_;
+    }
+};
+
+int key::count_;
+
+UNORDERED_AUTO_TEST(transparent_count) {
+    key::count_ = 0;
+
+    struct hasher {
+        std::size_t operator()(key const& k) const {
+            return boost::hash<int>()(k.x_);
+        }
+
+        std::size_t operator()(int const k) const {
+            return boost::hash<int>()(k);
+        }
+    };
+
+    struct key_equal {
+        bool operator()(key const& k1, key const& k2) const {
+            return k1.x_ == k2.x_;
+        }
+
+        bool operator()(key const& k1, int const x) const {
+            return k1.x_ == x;
+        }
+
+        bool operator()(int const x, key const& k1 ) const {
+            return k1.x_ == x;
+        }
+    };
+
+    boost::unordered_map<key, int, hasher, key_equal> map;
+    map.insert({key(0), 1337});
+    BOOST_TEST(key::count_ == 1);
+
+    std::size_t const count = map.count(0);
+
+    BOOST_TEST(count == 1);
+    BOOST_TEST(key::count_ == 1);
+}
+
+RUN_TESTS()