Luna/libos/include/os/Action.h

/**
 * @file Action.h
 * @author apio (cloudapio.eu)
 * @brief Wrapper for callable objects, like function pointers or lambdas.
 *
 * @copyright Copyright (c) 2023, the Luna authors.
 *
 */

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

namespace os
{
    /**
     * @brief Wrapper for callable objects.
     *
     * Certain callable types such as capture lambdas don't have a named type, thus they can't be passed to functions as
     * arguments. The Action type acts as a callable wrapper for such functions, allowing them to be passed as arguments
     * to any function.
     */
    class Action
    {
      public:
        /**
         * @brief Construct a new empty Action object.
         *
         * Since it is not wrapping any callable object, this object is invalid and attempting to invoke its
         * (nonexistent) callable object will result in a crash at runtime.
         */
        Action()
        {
            m_action = nullptr;
        }

        /**
         * @brief Construct a new Action object, moving it from another one.
         *
         * @param other The old Action object to move from. This object will become invalid.
         */
        Action(Action&& other) : m_action(other.m_action)
        {
            other.m_action = nullptr;
        }

        /**
         * @brief Construct a new Action object from a callable object.
         *
         * @tparam T The type of the callable object. Since this can be guessed by template deduction, the object
         * doesn't actually need a type name.
         * @param function The callable object to wrap.
         */
        template <typename T> Action(T&& function)
        {
            m_action = new (std::nothrow) ActionImpl<T>(move(function));
        }

        /**
         * @brief Assign a new callable object to this Action.
         *
         * @tparam T The type of the callable object. Since this can be guessed by template deduction, the object
         * doesn't actually need a type name.
         * @param function The callable object to wrap.
         * @return Action& A reference to this object, as required by operator=().
         */
        template <typename T> Action& operator=(T&& function)
        {
            if (m_action) delete m_action;
            m_action = new (std::nothrow) ActionImpl<T>(move(function));
            return *this;
        }

        /**
         * @brief Call the underlying object.
         */
        void operator()()
        {
            expect(m_action, "os::Action called with no underlying callable object");
            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;
    };
}