Re: passing ref to ptr again as ref to ptr....

From:

"Bo Persson" <bop@gmb.dk>

Newsgroups:

comp.lang.c++

Date:

Thu, 24 Apr 2008 23:53:33 +0200

Message-ID:

<67cdqgF2oaglbU1@mid.individual.net>

osama178@gmail.com wrote:

On Apr 24, 2:32 pm, "Bo Persson" <b...@gmb.dk> wrote:

osama...@gmail.com wrote:

Let's say I have this code

--------------------
class GenericQueue
{
public:
       bool Pop(void*& refToPtr); //--------------(1)

};

class SpecialQueue: private GenericQueue
{
public:
       bool Pop(T*& refToPtr)
       {
               return
GenericQueue::Pop(refToPtr); //--------------------(2)
       }

};

Why does the statement in (2) generate an error?

You just cannot convert a reference to one type into a refererence
to another type, unless the latter is a base class of the first.

There is no guarantee that all T* must be the same size as a void*.

Bo Persson

Does that mean references and templates are not to be mixed?

No, they work very well together. I think the void* is the problem
here, and that you are trying too hard to optimize the code.

I would trust my compiler here, and just write

template<class T>
class GenericQueue
{
bool Pop(T&);

};

if that is the interface needed (it probably is not - take a look at
std::queue and std::stack).

The compiler knows which types (pointers or not) are of the same size,
and can compile that to identical code.

And
is that why STL containers do not store references to objects?

Many containers will have to copy some of their contents when
inserting or erasing members. References cannot be copied.

Bo Persson