I have a working Cloneable/CloneableImpl
class pair below. It does its job as long as I have default constructors from child to parent.
Suppose Animal's constructor is modified to Animal( std::string const& name )
, which needs the name to be passed up from the children class constructors.
How can I incorporate this requirement into the structure while keeping Cloneable/CloneableImpl
generic?
In other words, I need to be able forward all constructor arguments from Lion, Tiger up to Animal. Is there a way to do this in C++11 in a generic manner?
If it's not possible, how can these templates be restructured to remain generic while allowing for the constructor requirement?
Code
template<typename P>
struct Cloneable
{
virtual P* clone() const = 0;
};
template<typename T,typename P>
struct CloneableImpl :
public P
{
virtual P* clone() const
{
return new T( dynamic_cast<T const&>(*this));
}
};
// ----------------------------------------------------------------------------
struct Animal :
public Cloneable<Animal>
{
};
struct Lion :
public CloneableImpl<Lion,Animal>
{
};
struct Tiger :
public CloneableImpl<Tiger,Animal>
{
};
int
main( int argv, char* argc[] )
{
Animal* x = new Lion;
Animal* y = x->clone();
// we want to do this without hard-coding in template classes
// Animal* z = new Lion( "Samba" );
}
Following @Cheersandhth.-Alf and @R. Martinho Fernandes' suggestions in the Comments to the OP to look into perfect forwarding. I researched a bit and came up with this, which seems to work.
Thanks guys!
CODE
#include <string>
#include <iostream>
template<typename P>
struct Cloneable
{
virtual P* clone() const = 0;
};
template<typename T,typename P>
struct CloneableImpl :
public P
{
template<typename... Args>
CloneableImpl( Args&&... args )
: P(std::forward<Args>(args)...)
{ }
virtual P* clone() const
{
return new T( dynamic_cast<T const&>(*this));
}
};
// ----------------------------------------------------------------------------
struct Animal :
public Cloneable<Animal>
{
Animal( std::string const& name ) : m_name( name ) { }
std::string m_name;
};
struct Lion :
public CloneableImpl<Lion,Animal>
{
template<typename... Args>
Lion( Args&&... args )
: CloneableImpl<Lion,Animal>(std::forward<Args>(args)...)
{ }
};
struct Tiger :
public CloneableImpl<Tiger,Animal>
{
};
int
main( int argv, char* argc[] )
{
Animal* x = new Lion( "Samba" );
Animal* y = x->clone();
std::cerr << y->m_name << std::endl;
}
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