File content as of revision 74:8cb1c4aa4527:

/*
The MIT License (MIT)

Copyright (c) 2016 British Broadcasting Corporation.
This software is provided by Lancaster University by arrangement with the BBC.

Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the "Software"),
to deal in the Software without restriction, including without limitation
the rights to use, copy, modify, merge, publish, distribute, sublicense,
and/or sell copies of the Software, and to permit persons to whom the
Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.
*/

#ifndef MICROBIT_MANAGED_TYPE_H
#define MICROBIT_MANAGED_TYPE_H

#include "MicroBitConfig.h"

/**
  * Class definition for a Generic Managed Type.
  *
  * Represents a reference counted object.
  *
  * @note When the destructor is called, delete is called on the object - implicitly calling the given objects destructor.
  */
template <class T>
class ManagedType
{
protected:

    int *ref;

public:

    T *object;

    /**
      * Constructor for the managed type, given a class space T.
      *
      * @param object the object that you would like to be ref counted - of class T
      *
      * @code
      * T object = new T();
      * ManagedType<T> mt(t);
      * @endcode
      */
    ManagedType(T* object);

    /**
      * Default constructor for the managed type, given a class space T.
      */
    ManagedType();

    /**
      * Copy constructor for the managed type, given a class space T.
      *
      * @param t another managed type instance of class type T.
      *
      * @code
      * T* object = new T();
      * ManagedType<T> mt(t);
      * ManagedType<T> mt1(mt);
      * @endcode
      */
    ManagedType(const ManagedType<T> &t);

    /**
      * Destructor for the managed type, given a class space T.
      */
    ~ManagedType();

    /**
      * Copy-assign member function for the managed type, given a class space.
      *
      * @code
      * T* object = new T();
      * ManagedType<T> mt(t);
      * ManagedType<T> mt1 = mt;
      * @endcode
      */
    ManagedType<T>& operator = (const ManagedType<T>&i);

    /**
      * Returns the references to this ManagedType.
      *
      * @code
      * T* object = new T();
      * ManagedType<T> mt(t);
      * ManagedType<T> mt1(mt);
      *
      * mt.getReferences // this will be 2!
      * @endcode
      */
    int getReferences();

    /**
      * De-reference operator overload. This makes modifying ref-counted POD
      * easier.
      *
      * @code
      * ManagedType<int> x = 0;
      * *x = 1; // mutates the ref-counted integer
      * @endcode
      */
    T& operator*() {
        return *object;
    }

    /**
      * Method call operator overload. This forwards the call to the underlying
      * object.
      *
      * @code
      * ManagedType<T> x = new T();
      * x->m(); // resolves to T::m
      */
    T* operator->() {
        if (object == NULL)
            microbit_panic(MICROBIT_NULL_DEREFERENCE);
        return object;
    }

    /**
      * Shorthand for `x.operator->()`
      */
    T* get() {
        return object;
    }

    /**
      * A simple inequality overload to compare two ManagedType instances.
      */
    bool operator!=(const ManagedType<T>& x) {
        return !(this == x);
    }

    /**
      * A simple equality overload to compare two ManagedType instances.
      */
    bool operator==(const ManagedType<T>& x) {
        return this->object == x.object;
    }
};

/**
  * Constructor for the managed type, given a class space T.
  *
  * @param object the object that you would like to be ref counted - of class T
  *
  * @code
  * T object = new T();
  * ManagedType<T> mt(t);
  * @endcode
  */
template<typename T>
ManagedType<T>::ManagedType(T* object)
{
    this->object = object;
    ref = (int *)malloc(sizeof(int));
    *ref = 1;
}

/**
  * Default constructor for the managed type, given a class space T.
  */
template<typename T>
ManagedType<T>::ManagedType()
{
    this->object = NULL;
    ref = (int *)malloc(sizeof(int));
    *ref = 0;
}

/**
  * Copy constructor for the managed type, given a class space T.
  *
  * @param t another managed type instance of class type T.
  *
  * @code
  * T* object = new T();
  * ManagedType<T> mt(t);
  * ManagedType<T> mt1(mt);
  * @endcode
  */
template<typename T>
ManagedType<T>::ManagedType(const ManagedType<T> &t)
{
    this->object = t.object;
    this->ref = t.ref;
    (*ref)++;
}

/**
  * Destructor for the managed type, given a class space T.
  */
template<typename T>
ManagedType<T>::~ManagedType()
{
    // Special case - we were created using a default constructor, and never assigned a value.
    if (*ref == 0)
    {
        // Simply destroy our reference counter and we're done.
        free(ref);
    }

    // Normal case - we have a valid piece of data.
    // Decrement our reference counter and free all allocated memory if we're deleting the last reference.
    else if (--(*ref) == 0)
    {
        delete object;
        free(ref);
    }
}

/**
  * Copy-assign member function for the managed type, given a class space.
  *
  * @code
  * T* object = new T();
  * ManagedType<T> mt(t);
  * ManagedType<T> mt1 = mt;
  * @endcode
  */
template<typename T>
ManagedType<T>& ManagedType<T>::operator = (const ManagedType<T>&t)
{
    if (this == &t)
        return *this;

    // Special case - we were created using a default constructor, and never assigned a value.
    if (*ref == 0)
    {
        // Simply destroy our reference counter, as we're about to adopt another.
        free(ref);
    }

    else if (--(*ref) == 0)
    {
        delete object;
        free(ref);
    }

    object = t.object;
    ref = t.ref;

    (*ref)++;

    return *this;
}

/**
  * Returns the references to this ManagedType.
  *
  * @code
  * T* object = new T();
  * ManagedType<T> mt(t);
  * ManagedType<T> mt1(mt);
  *
  * mt.getReferences // this will be 2!
  * @endcode
  */
template<typename T>
int ManagedType<T>::getReferences()
{
    return (*ref);
}
#endif