Strong Typed generic Composite class

From:
ManicQin <ManicQin@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Thu, 17 Jul 2008 07:02:21 -0700 (PDT)
Message-ID:
<2b39b270-8709-4f30-9486-42960962a515@2g2000hsn.googlegroups.com>
Hello everyone and especially Kai-Uwe Bux
A month ago I post a question in the same name of this one but I didnt
managed to explain my question right, so people didn't understand me.
Now when I have the time to post it again I hope I could manage to
explain my self + to post the answer to my previous question.

So...
When you look at the Composite GOF pattern it's basically

//Snip
class Interface
{
  virtual void work() = 0;
}

class compositor : public Interface
{
  void work()
{ //Iterate through all the instances that the
   //Class holds and call their work function
}
 void addItem(Interface* newItem)
{ //you get the point }

vector<Interface*> m_Items
};
class workerA : public Interface {}
class workerB : public Interface {}
//Snip

If you want to add a new different class that inherits from a new
different Interface you will need to Copy Paste a new compositor.
If you want to Generalize the compositor you are heading to the
problem of how to keep it strong typed.
You can always use a master Object that all object are descendants of
him but you
will loose the strong type characteristic.
You can create a all purpose compositor but than you loose the
polymorphism of the classes
(If your interface "working" function is go() and your compositor
"working" function is Iterate() you cannot use a pointer to the
interface to handle a compositor (thus loosing the point))
OK so I patched up a Strong Typed Generic Compositor I added the code
at the end
(BTW works on VS2008 Express but not on VS6)

My new problem is how to further generalize the function call,
I have two solutions
1) To add a template for each possible function
A template for a function that returns void and 1 arg
A template for a function that -""- -""- and 2 args
and so one .. I've seen it many time but I dislike this solution
2) To add another level of abstraction and to patch up
classes for retVals and argVals (a bit of meta programming)

What do you think is better

//snip
#include <iostream>
#include <vector>

using namespace std;

#define CALL_MEMBER_FN(object,ptrToMember) ((object).*(ptrToMember))

class IWorker
{
public:
    virtual void work() = 0;
};

class ILaborer
{
public:
    virtual void labor() = 0;
};

template <class T,void (T::*funcPtr)()>
class ABCCompositor
{
public:
    typedef vector<T*> tItemVec;

    void addItem(T* newItem)
    {
        m_ItemCol.push_back(newItem);
    }

    void IterateThrough()
    {
        for (tItemVec::iterator iDx = m_ItemCol.begin();
            iDx < m_ItemCol.end(); iDx++)
        {
            CALL_MEMBER_FN(*(*iDx),funcPtr)();
        }
    }

protected:
    tItemVec m_ItemCol;
};

class WorkerCompositor : public IWorker,
    public ABCCompositor<IWorker,&IWorker::work>
{
public:

    void work()
    {
        IterateThrough();
    }
};

class LaborerCompositor : public ILaborer,
    public ABCCompositor<ILaborer,&ILaborer::labor>
{
public:

    void labor()
    {
        IterateThrough();
    }
};

class CPrinter : public IWorker
{
public:
    void work()
    {
        cout << "Hello" << endl;
    }
};
class CPrinter2 : public IWorker
{
public:
    void work()
    {
        cout << " OLA!!!" << endl;
    }
};

class CPrinter3 : public ILaborer
{
public:
    void labor()
    {
        cout << "Shalom" << endl;
    }
};
class CPrinter4 : public ILaborer
{
public:
    void labor()
    {
        cout << "Salam" << endl;
    }
};

int main()
{

    WorkerCompositor printSession1;
    WorkerCompositor printSession2;

    printSession1.addItem(new CPrinter);
    printSession1.addItem(new CPrinter2);
    printSession1.addItem(new CPrinter);
    printSession1.addItem(new CPrinter2);
    printSession1.addItem(new CPrinter);
    printSession2.addItem(&printSession1);
    printSession2.addItem(new CPrinter2);

    printSession2.work();

    LaborerCompositor printSession3;
    LaborerCompositor printSession4;

    printSession3.addItem(new CPrinter3);
    printSession3.addItem(new CPrinter4);
    printSession3.addItem(new CPrinter3);
    printSession3.addItem(new CPrinter4);
    printSession3.addItem(new CPrinter3);
    printSession4.addItem(&printSession3);
    printSession4.addItem(new CPrinter3);

    printSession4.labor();
    return 0;
}

//snip

Thanks

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