{
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  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<p style=\"float: left;\"><a href=\"unified-types.ipynb\" target=\"_blank\">Previous</a></p>\n",
    "<p style=\"float: right;\"><a href=\"traits.ipynb\" target=\"_blank\">Next</a></p>\n",
    "<p style=\"text-align:center;\">Tour of Scala</p>\n",
    "<div style=\"clear: both;\"></div>\n",
    "\n",
    "# Classes\n",
    "\n",
    "Classes in Scala are blueprints for creating objects. They can contain methods,\n",
    "values, variables, types, objects, traits, and classes which are collectively called _members_. Types, objects, and traits will be covered later in the tour.\n",
    "\n",
    "## Defining a class\n",
    "A minimal class definition is simply the keyword `class` and\n",
    "an identifier. Class names should be capitalized."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
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      "tut"
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   "outputs": [
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     "data": {
      "text/plain": [
       "defined \u001b[32mclass\u001b[39m \u001b[36mUser\u001b[39m\n",
       "\u001b[36muser1\u001b[39m: \u001b[32mUser\u001b[39m = ammonite.$sess.cmd0$Helper$User@75e7dbbd"
      ]
     },
     "execution_count": 1,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "class User\n",
    "\n",
    "val user1 = new User"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The keyword `new` is used to create an instance of the class. `User` has a default constructor which takes no arguments because no constructor was defined. However, you'll often want a constructor and class body. Here is an example class definition for a point:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
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      "tut"
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   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "(2, 3)\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "defined \u001b[32mclass\u001b[39m \u001b[36mPoint\u001b[39m\n",
       "\u001b[36mpoint1\u001b[39m: \u001b[32mPoint\u001b[39m = (2, 3)\n",
       "\u001b[36mres1_2\u001b[39m: \u001b[32mInt\u001b[39m = \u001b[32m2\u001b[39m"
      ]
     },
     "execution_count": 2,
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     "output_type": "execute_result"
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   ],
   "source": [
    "class Point(var x: Int, var y: Int) {\n",
    "\n",
    "  def move(dx: Int, dy: Int): Unit = {\n",
    "    x = x + dx\n",
    "    y = y + dy\n",
    "  }\n",
    "\n",
    "  override def toString: String =\n",
    "    s\"($x, $y)\"\n",
    "}\n",
    "\n",
    "val point1 = new Point(2, 3)\n",
    "point1.x  // 2\n",
    "println(point1)  // prints (2, 3)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This `Point` class has four members: the variables `x` and `y` and the methods `move` and\n",
    "`toString`. Unlike many other languages, the primary constructor is in the class signature `(var x: Int, var y: Int)`. The `move` method takes two integer arguments and returns the Unit value `()`, which carries no information. This corresponds roughly with `void` in Java-like languages. `toString`, on the other hand, does not take any arguments but returns a `String` value. Since `toString` overrides `toString` from [`AnyRef`](unified-types.ipynb), it is tagged with the `override` keyword.\n",
    "\n",
    "## Constructors\n",
    "\n",
    "Constructors can have optional parameters by providing a default value like so:"
   ]
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  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "attributes": {
     "classes": [
      "tut"
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    }
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   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1\n"
     ]
    },
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     "data": {
      "text/plain": [
       "defined \u001b[32mclass\u001b[39m \u001b[36mPoint\u001b[39m\n",
       "\u001b[36morigin\u001b[39m: \u001b[32mPoint\u001b[39m = ammonite.$sess.cmd2$Helper$Point@7c93be3e\n",
       "\u001b[36mpoint1\u001b[39m: \u001b[32mPoint\u001b[39m = ammonite.$sess.cmd2$Helper$Point@2643ecab"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "class Point(var x: Int = 0, var y: Int = 0)\n",
    "\n",
    "val origin = new Point  // x and y are both set to 0\n",
    "val point1 = new Point(1)\n",
    "println(point1.x)  // prints 1\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "In this version of the `Point` class, `x` and `y` have the default value `0` so no arguments are required. However, because the constructor reads arguments left to right, if you just wanted to pass in a `y` value, you would need to name the parameter."
   ]
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   "cell_type": "code",
   "execution_count": 4,
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    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "2\n"
     ]
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       "defined \u001b[32mclass\u001b[39m \u001b[36mPoint\u001b[39m\n",
       "\u001b[36mpoint2\u001b[39m: \u001b[32mPoint\u001b[39m = ammonite.$sess.cmd3$Helper$Point@4fe09999"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "class Point(var x: Int = 0, var y: Int = 0)\n",
    "val point2 = new Point(y=2)\n",
    "println(point2.y)  // prints 2"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This is also a good practice to enhance clarity.\n",
    "\n",
    "## Private Members and Getter/Setter Syntax\n",
    "Members are public by default. Use the `private` access modifier\n",
    "to hide them from outside of the class."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
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      "tut"
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   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "WARNING: Out of bounds\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "defined \u001b[32mclass\u001b[39m \u001b[36mPoint\u001b[39m\n",
       "\u001b[36mpoint1\u001b[39m: \u001b[32mPoint\u001b[39m = ammonite.$sess.cmd4$Helper$Point@3e08416e"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
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   ],
   "source": [
    "class Point {\n",
    "  private var _x = 0\n",
    "  private var _y = 0\n",
    "  private val bound = 100\n",
    "\n",
    "  def x = _x\n",
    "  def x_= (newValue: Int): Unit = {\n",
    "    if (newValue < bound) _x = newValue else printWarning\n",
    "  }\n",
    "\n",
    "  def y = _y\n",
    "  def y_= (newValue: Int): Unit = {\n",
    "    if (newValue < bound) _y = newValue else printWarning\n",
    "  }\n",
    "\n",
    "  private def printWarning = println(\"WARNING: Out of bounds\")\n",
    "}\n",
    "\n",
    "val point1 = new Point\n",
    "point1.x = 99\n",
    "point1.y = 101 // prints the warning"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "In this version of the `Point` class, the data is stored in private variables `_x` and `_y`. There are methods `def x` and `def y` for accessing the private data. `def x_=` and `def y_=` are for validating and setting the value of `_x` and `_y`. Notice the special syntax for the setters: the method has `_=` appended to the identifier of the getter and the parameters come after.\n",
    "\n",
    "Primary constructor parameters with `val` and `var` are public. However, because `val`s are immutable, you can't write the following."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
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     ],
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   },
   "outputs": [
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "cmd5.sc:3: reassignment to val\n",
      "val res5_2 = point.x = 3  // <-- does not compile\n",
      "                     ^Compilation Failed"
     ]
    },
    {
     "ename": "",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "Compilation Failed"
     ]
    }
   ],
   "source": [
    "class Point(val x: Int, val y: Int)\n",
    "val point = new Point(1, 2)\n",
    "point.x = 3  // <-- does not compile"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Parameters without `val` or `var` are private values, visible only within the class."
   ]
  },
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   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "attributes": {
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      "tut"
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     "id": ""
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   },
   "outputs": [
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "cmd5.sc:3: value x is not a member of Helper.this.Point\n",
      "val res5_2 = point.x  // <-- does not compile\n",
      "                   ^Compilation Failed"
     ]
    },
    {
     "ename": "",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "Compilation Failed"
     ]
    }
   ],
   "source": [
    "class Point(x: Int, y: Int)\n",
    "val point = new Point(1, 2)\n",
    "point.x  // <-- does not compile"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<p style=\"float: left;\"><a href=\"unified-types.ipynb\" target=\"_blank\">Previous</a></p>\n",
    "<p style=\"float: right;\"><a href=\"traits.ipynb\" target=\"_blank\">Next</a></p>\n",
    "<p style=\"text-align:center;\">Tour of Scala</p>\n",
    "<div style=\"clear: both;\"></div>"
   ]
  }
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