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C ++ Cloneable mixin

I have several classes that require the following function clone:

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

struct A : public Base
{
    Base * clone() const {
      return new A(*this);
  }
};

struct B : public Base
{
    Base * clone() const {
      return new B(*this);
  }
};

struct X : public Base2
{
    Base2 * clone() const {
      return new X(*this);
  }
};

I am trying to do this with a Cloneable mixin to avoid this redundant code:

template <typename BASE, typename TYPE>
class CloneableMixin
{
public:
  BASE*clone() const {
    return new TYPE( dynamic_cast<const TYPE &>(*this) );
  }
};

struct A : public Base, public CloneableMixin<Base, A>
{
};

However, this does not work, because new TYPE(*this)of CloneableMixin, *thishas a type CloneableMixin<BASE, TYPE>.

You CloneableMixin can dynamic_castupgrade to the desired type. But now I have another problem: it CloneableMixin::clonedoes not override the override Base::clone, so the compiler A reports are abstract.

Can any clever use of inheritance virtualallow CloneableMixin::cloneoverriding Base::clone? Is there some kind of macro that I should use for this?

Do you know a way to get around all this redundant code?

+5
source
2

- CloneableMixin:: clone Base:: clone?

CloneableMixin<Base,Derived> Base - - CloneableMixin<Base,Derived> Base.

, CloneableMixin<Base,Derived> Base , -

class Derived : public CloneableMixin<Base,Derived> {....};

Base.

, :

#include <iostream>

// cloner v1.0
template <class Base, class Derived>
struct cloner : Base
{
    Base *clone() const override {
        return new Derived( dynamic_cast<const Derived &>(*this) );
    }
    ~cloner() override {};
};

struct Base
{
    virtual Base * clone() const = 0;
    Base() {
        std::cout << "Base()" << std::endl;
    }
    virtual ~Base() {
        std::cout << "~Base()" << std::endl;
    }
};


struct A : cloner<Base,A> 
{
    A() {
        std::cout << "A()" << std::endl;
    }
    ~A() override {
        std::cout << "~A()" << std::endl;
    }
};

int main()
{
    A a;
    Base * pb = a.clone();
    delete pb;
}

( ++ 03, ++ 11, override.)

, :

#include <iostream>
#include <memory>

using namespace std;

// cloner v1.0
template<class B, class D>
struct cloner : B
{
    B *clone() const override {
        return new D(dynamic_cast<D const&>(*this));
    }
    ~cloner() override {}       
};

/*  Abstract base class `abstract` keeps the state for all derivatives
    and has some pure virtual methods. It has some non-default
    constructors. 
*/
struct abstract 
{
    virtual ~abstract() {
        cout << "~abstract()" << endl;
    }
    int get_state() const {
        return _state;
    }
    void run() {
        cout << "abstract::run()" << endl;
        a_root_method();
        another_root_method();
    }
    virtual void a_root_method() = 0;
    virtual void another_root_method() = 0;
    virtual abstract * clone() const = 0;

protected:

    abstract()
    : _state(0) {
        cout << "abstract(): state = " << get_state() << endl;
    }
    explicit abstract(int state) : _state(state) {
        cout << "abstract(" << state << ") : state = " 
        << get_state() << endl;
    }   
    int _state;
};

/*  Concrete class `concrete` inherits `abstract`
    and implements the pure virtual methods.
    It echoes the constructors of `abstract`. Since `concrete`
    is concrete, it requires cloneability. 
*/
struct concrete : cloner<abstract,concrete> 
{   
    concrete() { 
        cout << "concrete(): state = " << get_state() << endl;
    }
    explicit concrete(int state) : abstract(state) {  //<- Barf!
        cout << "concrete(" << state << ") : state = " 
            << get_state() << endl;
    }
    ~concrete() override {
        cout << "~concrete()" << endl;
    }
    void a_root_method() override {
        ++_state; 
        cout << "concrete::a_root_method() : state = " 
            << get_state() << endl;
    }
    void another_root_method() override {
        --_state;
        cout << "concrete::another_root_method() : state = " 
            << get_state() << endl;
    }       
};

int main(int argc, char **argv)
{
    concrete c1;
    unique_ptr<abstract> pr(new concrete(c1));
    pr->a_root_method();
    pr->another_root_method();
    unique_ptr<abstract> pr1(pr->clone());
    pr1->a_root_method();
    return 0;
}

, abstract(state) concrete ( Barf! ), :

error: type 'abstract' is not a direct or virtual base of 'concrete'

. , concrete abstract cloner<abstract,concrete>. :

/*Plan B*/ explicit concrete(int state) : cloner<abstract,concrete>(state){....}

,

cloner<abstract,concrete>::cloner<abstract,concrete>(int)

. . abstract concrete, " concrete", B cloner<B,D>:

// cloner v1.1
template<class B, class D>
struct cloner : virtual B
{
    B *clone() const override {
        return new D(dynamic_cast<D const&>(*this));
    }
    ~cloner() override {}       
};

:

abstract(): state = 0
concrete(): state = 0
concrete::a_root_method() : state = 1
concrete::another_root_method() : state = 0
concrete::a_root_method() : state = 1
~concrete()
~abstract()
~concrete()
~abstract()
~concrete()
~abstract()

, , , , - , .

, - , cloner<B,D>, B, B. D cloner<B,D> .

++ 03, ++ 11 :

// cloner v1.2
template<class B, class D>
struct cloner : B
{
    B *clone() const override {
        return new D(dynamic_cast<D const&>(*this));
    }
    ~cloner() override {}
    // "All purpose constructor"
    template<typename... Args>
    explicit cloner(Args... args)
    : B(args...){}  
};

concrete /*Plan B*/, .

+4

Cloneable mixin . :

template 
<
    typename Derived
>
class Cloneable 
:    
    private CloneableBase
{
public:
    Derived* clone() const
    {
        return static_cast<Derived*>(this->do_clone());
    }

private:
    virtual Cloneable* do_clone() const
    {
        return new Derived(static_cast<const Derived&>(*this));
    }
};

class CloneableBase
{
public:
    CloneableBase* clone() const
    {
        return do_clone();
    }

private:
    virtual CloneableBase* do_clone() const=0;
};

class MyClass: public Cloneable<MyClass>;
0

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