Entity: Add placement new

For the case where the component may already exist, use a placement new to construct the component again, it would be constructed again, but would not need to go through the allocator.

dGame/Entity.h

@@ -523,6 +523,10 @@ inline ComponentType* Entity::AddComponent(VaArgs... args) {
 	// If it doesn't exist, create it and forward the arguments to the constructor
 	if (!componentToReturn) {
 		componentToReturn = new ComponentType(this, std::forward<VaArgs>(args)...);
+	} else {
+		// In this case the block is already allocated and ready for use
+		// so we use a placement new to construct the component again as was requested by the caller.
+		new(componentToReturn) ComponentType(this, std::forward<VaArgs>(args)...);
 	}
 
 	// Finally return the created or already existing component.

tests/dGameTests/dComponentsTests/DestroyableComponentTests.cpp

@@ -36,6 +36,14 @@ class DestroyableTest : public GameDependenciesTest {
 	}
 };
 
+TEST_F(DestroyableTest, PlacementNewAddComponentTest) {
+	ASSERT_NE(destroyableComponent, nullptr);
+	ASSERT_EQ(destroyableComponent->GetArmor(), 7);
+	baseEntity->AddComponent<DestroyableComponent>();
+	ASSERT_NE(baseEntity->GetComponent<DestroyableComponent>(), nullptr);
+	ASSERT_EQ(destroyableComponent->GetArmor(), 0);
+}
+
 /**
  * Test Construction of a DestroyableComponent
  */