Re: Custom generic container class

From:
mos <moswald@gmail.com>
Newsgroups:
comp.lang.c++.moderated
Date:
Fri, 13 Nov 2009 14:42:53 CST
Message-ID:
<93829c08-3cc6-4e60-9e27-c64091d3abb3@j19g2000yqk.googlegroups.com>
On Nov 9, 8:53 am, Navaneeth <navaneet...@gmail.com> wrote:

I am trying to create a class named "tree_node" which can hold a label
(char) and any type of data. I came up with the following code.

template<typename T>
struct node_traits
{
     typedef T& reference;
     typedef T* pointer;

};

template<typename T>
struct node_traits<T*>
{
     typedef T* reference;
     typedef T* pointer;

};

template<typename T>
class tree_node
{
     public:
         typedef typename node_traits<T>::reference reference;
         typedef typename node_traits<T>::pointer pointer;

         tree_node(reference item)
         {
            //item_ = item; Works only if T is pointer
            item_ = new T(item);
         }

         reference item()
         {
             return item_;
         }

     private:

         pointer item_;

};

My intention here is to create a container that can hold any type of
object. Like STL, I would like to copy create the object for all non-
pointer types. The above code will not work as I expected. Consider
the following usages.

Foo f;
tree_node<Foo> node(f); // works well
tree_node<Foo*> node1(new Foo); // will not work until i change the
implementation of class

1 - How will I create the class in such way that it accepts all types.
2 - Is there anyway to keep the object inside the class without using
pointers?

I'd not be interested in any libraries that have such a class because
I am creating this just for learning.

Thanks


I haven't tested this fully, but it compiles just fine:<typename T>
class tree_node
{
    template<typename T>
    struct node_traits
    {
         typedef T& reference;
         typedef T* pointer;
         typedef T value_type;
    };

    // specialized for pointer
    template<typename T>
    struct node_traits<T*>
    {
         typedef T* reference;
         typedef T* pointer;
         typedef T* value_type;
    };

    // specialized for reference
    template<typename T>
    struct node_traits<T&>
    {
         typedef T& reference;
         typedef T* pointer;
         typedef T& value_type;
    };

public:
    typedef typename node_traits<T>::reference reference;
    typedef typename node_traits<T>::pointer pointer;
    typedef typename node_traits<T>::value_type value_type;

    tree_node(reference item)
        : item_(item)
    {
    }

    reference item()
    {
        return item_;
    }

private:
    value_type item_;
};

int x = 10;
tree_node<int> copied_node(x);
tree_node<int *> ptr_node(new int(11));
tree_node<int &> ref_node(x);

--m

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