Here's a Clone()
implementation for my class:
MyClass^ Clone(){
return gcnew MyClass(this->member1, this->member2);
}
Now I have about 10 classes derived from MyClass
. The implementation is the same in each case. Owing to the fact that I need to call gcnew
with the actual class name in each case, I am required to create 10 nearly identical implementations of Clone()
.
Is there a way to write one single Clone()
method in the base class which will serve all 10 derived classes?
Edit: Is there a way to invoke the constructor of a class via one of it's objects? In a way that will invoke the actual derived class constructor. Something like:
MyClass ^obj2 = obj1->Class->Construct(arg1, arg2);
I'm doing this on C++/CLI but answers from other languages are welcome.
In plain old C++, you can do this with compile-time polymorphism (the curiously-recurring template pattern). Assuming your derived classes are copyable, you can just write:
class Base
{
public:
virtual Base* Clone() const = 0;
//etc.
};
template <typename Derived>
class BaseHelper: public Base
{
//other base code here
//This is a covariant return type, allowed in standard C++
Derived * Clone() const
{
return new Derived(static_cast<Derived *>(*this));
}
};
Then use it like:
class MyClass: public BaseHelper<MyClass>
{
//MyClass automatically gets a Clone method with the right signature
};
Note that you can't derive from a class again and have it work seamlessly - you have to "design in" the option to derive again by templating the intermediate classes, or start re-writing Clone
again.