Diff: inc/types/ManagedType.h

Revision:

1:8aa5cdb4ab67

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/inc/types/ManagedType.h	Thu Apr 07 01:33:22 2016 +0100
@@ -0,0 +1,279 @@
+/*
+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