C++Talk.NET

Charles-Antoine Giuliani · Guest

Is it possible to implement a Clone() function via a template?

If I have a protocol class
class PVClass {
public:
virtual PVClass* Clone(void) = 0;
};

and I want a handle class
class ImplClass : public PVClass {
public:
virtual ImplClass* Clone(void) { return new ImplClass(*this);};
}

but I do not want to rewrite the Clone function for all derived
classes so that I can hide the code in a library and by the way add
other related functions... Is there a way for me to write :
class ImplClass : public MakePVCompatible<ImplClass> {
};

I have tried the following solution but I think it is a hack and
runtime inefficient (but a dynamic cast is not really required...):
template <class T> MakePVCompatible : public PVClass {
public:
virtual PVClass* Clone(void) { return (new T(*dynamic_cast<const
T*>(this))); };
};
It does work with Visual C++ 7.1 but does not allow me to use the
return type covariance (but I am using auto_ptr which I do not
completely master so they may be the problem for the covariance).

Is there a better solution ?

Thanks in advance,

Charles

[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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Maxim Yegorushkin · Guest

On 29 Dec 2004 03:49:00 -0500, Charles-Antoine Giuliani
<apprentice_99 (AT) hotmail (DOT) com> wrote:

Niels Dekker - no reply a · Guest

Charles-Antoine Giuliani wrote:

Stefan de Bruijn · Guest

Charles-Antoine Giuliani wrote:

Maxim Yegorushkin · Guest

Stefan de Bruijn wrote:

Vladimir Marko · Guest

Charles-Antoine Giuliani wrote:

DEX · Guest

Solution One:
template< typename T >
class PVClass {
public:
virtual T* Clone(void) = 0;
};

template < typename T>
class ImplClass : public PVClass< T> {
public:
ImplClass(){}
virtual T* Clone(void)
{
T *i = dynamic_cast<T*>(this);
if( NULL == i ) return NULL;
return new T(*i);
}
};

class MyFirst : public ImplClass <MyFirst>
{
public:
};

class MySecond : public ImplClass <MySecond>
{
public:
};

Solution Two:
class PVClass {
public:
virtual PVClass* Clone(void) = 0;
};

template < typename T>
class ImplClass : public PVClass {
public:
ImplClass(){}
virtual PVClass* Clone(void)
{
T *i = dynamic_cast<T*>(this);
if( NULL == i ) return NULL;
return new T(*i);
}
};

class MyFirst : public ImplClass <MyFirst>
{
public:
};

class MySecond : public ImplClass <MySecond>
{
public:
};

[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]

Stefan de Bruijn · Guest

Maxim Yegorushkin · Guest

Stefan de Bruijn wrote:

Your post had two solutions, I'll comment on both.

[]

The second solution was:

Stefan Strasser · Guest

Vladimir Marko schrieb:

Vladimir Marko · Guest

Stefan Strasser wrote:

Stefan Strasser · Guest

Vladimir Marko schrieb:

Vladimir Marko · Guest

Stefan Strasser wrote: