Add singledispatchmehtod example

Author: gjbex

source-code/object-orientation/overloading.ipynb

@@ -4,7 +4,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "# Overloading"
+    "# Introduction"
    ]
   },
   {
@@ -14,9 +14,16 @@
     "Although Python doesn't support function overloading directly, there is functionality for it via its standard library in the `functools` module."
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Requirements"
+   ]
+  },
   {
    "cell_type": "code",
-   "execution_count": 1,
+   "execution_count": 39,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -27,7 +34,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Simple example"
+    "# Simple example"
    ]
   },
   {
@@ -132,6 +139,147 @@
    "source": [
     "my_func(['a', 'b', 'c'], True)"
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Overloaded constructor example"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "For object methods, `functools` has the `singledispatchmethod` decorator.  The following class has an overloaded constructor that takes either two `float` values, a `Point` object, or a `tuple` to initialize the $x$ and $y$ coordinates of the point."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 78,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "class Point():\n",
+    "    \n",
+    "    @functools.singledispatchmethod\n",
+    "    def __init__(self):\n",
+    "        raise NotImplementedError\n",
+    "\n",
+    "    @__init__.register\n",
+    "    def _(self, x: float, y: float):\n",
+    "        self._x, self._y = x, y\n",
+    "        \n",
+    "    @property\n",
+    "    def x(self):\n",
+    "        return self._x\n",
+    "    \n",
+    "    @property\n",
+    "    def y(self):\n",
+    "        return self._y\n",
+    "    \n",
+    "    def __repr__(self):\n",
+    "        return f'({self.x}, {self.y})'\n",
+    "\n",
+    "@Point.__init__.register\n",
+    "def _(self, other: Point):\n",
+    "    self._x, self._y = other.x, other.y\n",
+    "    \n",
+    "@Point.__init__.register\n",
+    "def _(self, coords: tuple):\n",
+    "    self._x, self._y = coords"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Note that `tuple[float, float]` will not work since `issubclass` and `isinstance` do not accept parameterized generic types as their second arguments."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Specifying the $x$ and $y$ coordinates of the new point."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 79,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "(3.1, 5.3)"
+      ]
+     },
+     "execution_count": 79,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "p = Point(3.1, 5.3)\n",
+    "p"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Using an existing point to create a new one (copy constructor)."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 80,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "(3.1, 5.3)"
+      ]
+     },
+     "execution_count": 80,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "p2 = Point(p)\n",
+    "p2"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Specifying the coordinates as a tuple."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 83,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "(3.5, 9.3)"
+      ]
+     },
+     "execution_count": 83,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "p3 = Point((3.5, 9.3))\n",
+    "p3"
+   ]
   }
  ],
  "metadata": {
@@ -150,7 +298,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.7.5"
+   "version": "3.9.5"
   }
  },
  "nbformat": 4,