Polymorphism in C++ has usually been implemented through the use of an inheritance hierarchy and virtual function calls. This method while effective has one key drawback originating from the problem of multiple inheritance: a derived class having two or more parents can be the source of many ambiguities. The 'solution' to this problem was addressed by means of virtual inheritance: a technique used to prevent multiple instances of one class in an inheritance hierarchy. Although virtual inheritance fixes the diamond problem, it generates additional performance overhead and higher levels of complexity to a code base. An optimal alternative to the use of virtual inheritance is the concept of Mix-Ins, founded on the idea of granularity and composition.

DynaMix is a useful library that elaborates on the concept of Mix-Ins, letting the user compose and modify polymorphic objects at runtime. It provides users with an effective alternative to the commonly used approach of inheritance, while still not adding many of the nuances that come from the solution using virtual inheritance. The library encompasses the notion of composition by the use of a dynamix::object that can be mutated with any number of Mix-Ins. Its benefits show when dealing with larger projects that need the use of complex objects composed of multiple parts; an example of such project would be a game composed of entities that have different behaviors or characteristics that define them.

Here is a basic example of the library in action:

#include <dynamix/dynamix.hpp>
#include <iostream>

struct Label
{
    void display()
    {
        std::cout << "Label\n";
    }
};

struct Sprite
{
    void display()
    {
        std::cout << "Sprite\n";
    }
};

DYNAMIX_DECLARE_MIXIN(Label);
DYNAMIX_DECLARE_MIXIN(Sprite);

DYNAMIX_MESSAGE_0(void, display);

DYNAMIX_DEFINE_MIXIN(Label, display_msg);
DYNAMIX_DEFINE_MIXIN(Sprite, display_msg);

DYNAMIX_DEFINE_MESSAGE(display);

int main()
{
    dynamix::object object;

    dynamix::mutate(object).add<Label>();

    display(object);

    dynamix::mutate(object).remove<Label>().add<Sprite>();

    display(object);
}

Output:
Label
Sprite

DynaMix offers a different view to what polymorphism can look like. Mix-Ins are more flexible and effective in handling complex objects that depend on multiple traits, composition through the use of Mix-Ins is the prime alternative to what inheritance can offer.