Derived class to take arg that is also derived

[stav]

Hi

i have a base class with a pure virtual function called "add" that takes in a ref to a "base_struct"

i want any child class of "base" to have the function "add" and take in a child of "base_struct"

for example:

struct base_struct
{

};

struct child_of_base_struct : public base_struct
{

};

class base
{
   public:
      virtual void add(base_struct& base) = 0;

};

class child : public base
{
   public:
      void add(child_of_base_struct& child_base) override;

};

But when i run this, i get an error saying that the method "add" in "child" isn't overriding anything. So im guessing its simply not possible?

or is there another way to achieve this?

[Repeater]

struct base_struct
{

};

struct child_of_base_struct : public base_struct
{

};

class base
{
   public:
      virtual void add(child_of_base_struct& child_base) = 0;

};

class child : public base
{
   public:
      void add(child_of_base_struct& child_base) override;

};

[stav]

Thanks for the reply
But there are multiple classes that derive from base and they all have to take different structs :\

i just want to require every child class of "base class" to have a function "add" that takes in a struct that is a child of the "base_struct". (To ensure that they all have some "required" functionality")

For instance: "help" class's "add" function take in a help_struct, and "report" class's "add" function take in a "report_struct". And all the structs derive from "base_struct".

I'm not sure if this is possible without casting though
(which i would like to avoid because i dont want the function signatures to say that they take in a "base_struct" when really they are meant to take in a "help_struct")

[doug4]

From the parent class' perspective, why does the child need to have an "add" function? The parent only cares about a base& from its derived classes. Why not have an hierarchy like this? (Notice the protected function forces derived classes to provide their own public interface functions.)

struct base_struct {};

struct child_of_base_struct : public base_struct {};

class base
{
   protected:
      void add(base_struct& base);
};

class child : public base
{
   public:
      void add(child_of_base_struct& child_base) { base::add(child_base); }
};

Since every "child" class disallows most of the other derived structs, you can't have a virtual function that all derived classes use directly.