memory: added pocca/pocma/pocs utility functions

test/entt/core/memory.cpp

@@ -2,6 +2,20 @@
 #include <gtest/gtest.h>
 #include <entt/core/memory.hpp>
 
+struct test_allocator: std::allocator<int> {
+    using base = std::allocator<int>;
+    using propagate_on_container_copy_assignment = std::true_type;
+    using propagate_on_container_swap = std::true_type;
+
+    using std::allocator<int>::allocator;
+
+    test_allocator & operator=(const test_allocator &other) {
+        // necessary to avoid call suppression
+        base::operator=(other);
+        return *this;
+    }
+};
+
 TEST(Memory, ToAddress) {
     std::shared_ptr<int> shared = std::make_shared<int>();
     auto *plain = std::addressof(*shared);
@@ -9,3 +23,11 @@ TEST(Memory, ToAddress) {
     ASSERT_EQ(entt::to_address(shared), plain);
     ASSERT_EQ(entt::to_address(plain), plain);
 }
+
+TEST(Memory, PoccaPocmaAndPocs) {
+    test_allocator lhs, rhs;
+    // honestly, I don't even know how one is supposed to test such a thing :)
+    entt::propagate_on_container_copy_assignment(lhs, rhs);
+    entt::propagate_on_container_move_assignment(lhs, rhs);
+    entt::propagate_on_container_swap(lhs, rhs);
+}