Re: About cloning

{ Double spacing removed. -mod }

Mathias Gaunard wrote:


you could try the clone/release scenario with customized allocator.
quick draft attached.

#include <memory>
#include <cstdio>

struct Base
{
        virtual ~Base() = 0;
        virtual Base* clone() const = 0;
        virtual void release() = 0;
};

inline Base::~Base()
{
}

template < template < typename > class A >
struct Derived
:
        public Base
{
        typedef A< Derived > Allocator;

        explicit Derived( Allocator const& a = Allocator() )
        :
                allocator_( a )
        {
                std::printf( "Derived( self = %p )\n", this );
        }

        explicit Derived( Derived const& rhs )
        :
                allocator_( rhs.allocator_ )
        {
                std::printf( "Derived( self = %p, rhs = %p )\n", this,
&rhs );
        }

        ~Derived()
        {
                std::printf( "~Derived( self = %p )\n", this );
        }

        Base* clone() const
        {
                Derived* p = allocator_.allocate( 1 );
                allocator_.construct( p, *this );
                return p;
        }

        void release()
        {
                allocator_.destroy( this );
                allocator_.deallocate( this, 1 );
        }

        mutable Allocator allocator_;
};

int main()
{
        Derived< std::allocator > const d;
        Base* b = d.clone();
        b->release();
        return 0;
}

$ g++ cloning.cpp -O2 -Wall -Weffc++ -o cloning && ./cloning

Derived( self = 0x7fff3e5357c0 )
Derived( self = 0x602010, rhs = 0x7fff3e5357c0 )
~Derived( self = 0x602010 )
~Derived( self = 0x7fff3e5357c0 )

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