Searching for specific element in Composite pattern

Question

Suppose I have a simple composite pattern structure:

• abstract class User

• leaf class PersonalUser

• composite class GroupUser with a std::vector<User*> users container as its member variable

and a method bool GroupUser::findUser(User* u) which returns true if the user u is found in the users container (which naturally consists of other PersonalUser or GroupUser objects)

Now, I'd like to define that function recursively of course, so I need to go through each User in users vector, and compare with u , but I won't know if the User is a PersonalUser or GroupUser , so my question is:

Do I have to define a virtual function char User::returnType() which will tell me which type of User it is, or is there a better/smarter way to go down the tree and look for the User ?

ps there is of course a method like bool areEqual(User*, User*) by which we can compare users :)

Answer 1

You can add the FindUser member function as a virtual to the abstract class User, and make it return true if the user being searched for is the current user (Personal or Group).

In GroupUser you can override FindUser and delegate any call to all the contained Users if the User being searched for isn't the current GroupUser.

Answer 2

As MadKeithV said, you declare the virtual function findUser(User*u) in the interface, then:

bool
    User::findUser(User*u) {
        return u == this;
    }

and

GroupUser::findUser(User *u) {
    for (// loop on your users)
        if (currentUser.findUser(u))
            return true;
    }
}

Answer 3

You can use eg dynamic_cast<>() to check if a User* is really a GroupUser or not, like this:

GroupUser* groupUser = dynamic_cast<GroupUser*>(userPointer);

If it returns a null pointer, then userPointer is not a GroupUser .