Support enable_observer_from_this with derived classes

Author: cschreib

include/oup/observable_unique_ptr.hpp

@@ -15,6 +15,7 @@ template<typename T>
 class enable_observer_from_this;
 
 namespace details {
+
 struct control_block {
     enum flag_elements {
         flag_none = 0,
@@ -37,6 +38,7 @@ template<typename T, typename Deleter>
 struct ptr_and_deleter : Deleter {
     T* data = nullptr;
 };
+
 }
 
 /// Simple default deleter
@@ -78,6 +80,9 @@ struct placement_delete
 };
 
 namespace details {
+
+struct enable_observer_from_this_base {};
+
 template<typename T, typename Deleter = oup::default_delete<T>>
 class observable_unique_ptr_base {
 protected:
@@ -111,7 +116,7 @@ class observable_unique_ptr_base {
 
     /// Fill in the observer pointer for objects inheriting from enable_observer_from_this.
     void set_this_observer_() noexcept {
-        if constexpr (std::is_base_of_v<enable_observer_from_this<T>, T>) {
+        if constexpr (std::is_base_of_v<details::enable_observer_from_this_base, T>) {
             if (ptr_deleter.data) {
                 ptr_deleter.data->this_observer.set_data_(block, ptr_deleter.data);
                 ++block->refcount;
@@ -362,6 +367,7 @@ class observable_unique_ptr_base {
         return ptr_deleter.data != nullptr;
     }
 };
+
 }
 
 /// Unique-ownership smart pointer, can be observed by observer_ptr, ownership can be released.
@@ -1180,7 +1186,7 @@ bool operator!= (const observer_ptr<T>& first, const observer_ptr<U>& second) no
 *   type of smart pointer, then observer_from_this() will return nullptr.
 */
 template<typename T>
-class enable_observer_from_this {
+class enable_observer_from_this : public details::enable_observer_from_this_base {
     mutable observer_ptr<T> this_observer;
 
     // Friendship is required for assignment of the observer.

tests/runtime_tests.cpp

@@ -2961,6 +2961,28 @@ TEST_CASE("observer from this sealed", "[observer_from_this]") {
     REQUIRE(mem_track.double_del() == 0u);
 }
 
+TEST_CASE("observer from this derived", "[observer_from_this]") {
+    memory_tracker mem_track;
+
+    {
+        test_ptr_from_this_derived ptr{new test_object_observer_from_this_derived};
+        const test_ptr_from_this_derived& cptr = ptr;
+
+        test_optr_from_this optr_from_this = ptr->observer_from_this();
+        test_optr_from_this_const optr_from_this_const = cptr->observer_from_this();
+
+        REQUIRE(instances == 1);
+        REQUIRE(optr_from_this.expired() == false);
+        REQUIRE(optr_from_this_const.expired() == false);
+        REQUIRE(optr_from_this.get() == ptr.get());
+        REQUIRE(optr_from_this_const.get() == ptr.get());
+    }
+
+    REQUIRE(instances == 0);
+    REQUIRE(mem_track.leaks() == 0u);
+    REQUIRE(mem_track.double_del() == 0u);
+}
+
 TEST_CASE("observer from this after move", "[observer_from_this]") {
     memory_tracker mem_track;
 

tests/tests_common.hpp

@@ -42,6 +42,9 @@ struct test_object_observer_from_this :
     public test_object,
     public oup::enable_observer_from_this<test_object_observer_from_this> {};
 
+struct test_object_observer_from_this_derived :
+    public test_object_observer_from_this {};
+
 struct test_deleter {
     int state_ = 0;
 
@@ -79,8 +82,12 @@ using test_sptr_thrower = oup::observable_sealed_ptr<test_object_thrower>;
 using test_ptr_thrower_with_deleter = oup::observable_unique_ptr<test_object_thrower,test_deleter>;
 using test_ptr_from_this = oup::observable_unique_ptr<test_object_observer_from_this>;
 using test_sptr_from_this = oup::observable_sealed_ptr<test_object_observer_from_this>;
+using test_ptr_from_this_derived = oup::observable_unique_ptr<test_object_observer_from_this_derived>;
+using test_sptr_from_this_derived = oup::observable_sealed_ptr<test_object_observer_from_this_derived>;
 
 using test_optr = oup::observer_ptr<test_object>;
 using test_optr_derived = oup::observer_ptr<test_object_derived>;
 using test_optr_from_this = oup::observer_ptr<test_object_observer_from_this>;
 using test_optr_from_this_const = oup::observer_ptr<const test_object_observer_from_this>;
+using test_optr_from_this_derived = oup::observer_ptr<test_object_observer_from_this_derived>;
+using test_optr_from_this_derived_const = oup::observer_ptr<const test_object_observer_from_this_derived>;