Re: handles in C++

Carter wrote:
> Hi,
> 
> I am currently working on a project in C++ but I am somewhat unsure
> about how to implement the equivalent of C/Java style handles. I am
> curious about the correct idiomatic way to do this. My problem is as
> follows I have a set of elements which I want to update to a new value
> all at the same time. I figure I would use a handle for this.
> 
> In C this might be a T** handle. and possibly an array/linked list
> holding the pointers T* array[N]. What is the best way to do something
> like this in C++?

There are many C++ ways of doing this.  The technique I like the most is 
the one that gives you the greatest type safety.  A handle can usually 
refer to different types of "things" being handled so you try to build a 
class heirarchy.

class HandleBase
{
    protected:
    HandleType m_handle;

    public:
    HandleBase(HandleType i_handle)
      : m_handle( i_handle )
    {
    }

    virtual void Close()
    {
       ... close handle ...
    }

    virtual ~HandleBase()
    {
        Close();
    }

    // no copying ...
    private:
    HanldeBase(const HanldeBase &);
    HanldeBase operator=(const HanldeBase &);
};


Now, the question is, how do you manage HandleBase which is a simple 
matter of defining how you want them to behave.  I like managing them 
with shared pointers which means when all references to a handle go 
away, the handle is magically closed.

e.g.

std::vector<shared_ptr<HanldeBase> > handles;

handles.push_back( new HandleBase(handle) );