Luna/libui/include/ui/Action.h

#pragma once
#include <luna/Heap.h>

namespace ui
{
    class Action
    {
      public:
        Action()
        {
            m_action = nullptr;
        }

        Action(Action&& other) : m_action(other.m_action)
        {
            other.m_action = nullptr;
        }

        template <typename T> Action(T&& function)
        {
            m_action = new (std::nothrow) ActionImpl<T>(move(function));
        }

        template <typename T> Action& operator=(T&& function)
        {
            if (m_action) delete m_action;
            m_action = new (std::nothrow) ActionImpl<T>(move(function));
            return *this;
        }

        void operator()()
        {
            check(m_action);
            return m_action->call();
        }

        ~Action()
        {
            if (m_action) delete m_action;
        }

      private:
        class ActionBase
        {
          public:
            virtual void call() = 0;
            virtual ~ActionBase() = default;
        };

        template <typename T> class ActionImpl final : public ActionBase
        {
          public:
            ActionImpl(T&& function) : m_function(move(function))
            {
            }

            void call()
            {
                return m_function();
            }

          private:
            T m_function;
        };

        ActionBase* m_action;
    };
}