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    "<p style=\"float: left;\"><a href=\"implicit-parameters.ipynb\" target=\"_blank\">Previous</a></p>\n",
    "<p style=\"float: right;\"><a href=\"polymorphic-methods.ipynb\" target=\"_blank\">Next</a></p>\n",
    "<p style=\"text-align:center;\">Tour of Scala</p>\n",
    "<div style=\"clear: both;\"></div>\n",
    "\n",
    "# Implicit Conversions\n",
    "\n",
    "An implicit conversion from type `S` to type `T` is defined by an implicit value which has function type `S => T`, or by an implicit method convertible to a value of that type.\n",
    "\n",
    "Implicit conversions are applied in two situations:\n",
    "\n",
    "* If an expression `e` is of type `S`, and `S` does not conform to the expression's expected type `T`.\n",
    "* In a selection `e.m` with `e` of type `S`, if the selector `m` does not denote a member of `S`.\n",
    "\n",
    "In the first case, a conversion `c` is searched for which is applicable to `e` and whose result type conforms to `T`.\n",
    "In the second case, a conversion `c` is searched for which is applicable to `e` and whose result contains a member named `m`.\n",
    "\n",
    "If an implicit method `List[A] => Ordered[List[A]]` is in scope, as well as an implicit method `Int => Ordered[Int]`, the following operation on the two lists of type `List[Int]` is legal:"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "```scala\n",
    "List(1, 2, 3) <= List(4, 5)\n",
    "```\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "An implicit method `Int => Ordered[Int]` is provided automatically through `scala.Predef.intWrapper`. An example of an implicit method `List[A] => Ordered[List[A]]` is provided below."
   ]
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      "text/plain": [
       "\u001b[32mimport \u001b[39m\u001b[36mscala.language.implicitConversions\n",
       "\n",
       "\u001b[39m\n",
       "defined \u001b[32mfunction\u001b[39m \u001b[36mlist2ordered\u001b[39m"
      ]
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   "source": [
    "import scala.language.implicitConversions\n",
    "\n",
    "implicit def list2ordered[A](x: List[A])\n",
    "    (implicit elem2ordered: A => Ordered[A]): Ordered[List[A]] =\n",
    "  new Ordered[List[A]] { \n",
    "    //replace with a more useful implementation\n",
    "    def compare(that: List[A]): Int = 1\n",
    "  }"
   ]
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The implicitly imported object `scala.Predef` declares several aliases to frequently used types (e.g. `scala.collection.immutable.Map` is aliased to `Map`) and methods (e.g. `assert`) but also several implicit conversions.\n",
    "\n",
    "For example, when calling a Java method that expects a `java.lang.Integer`, you are free to pass it a `scala.Int` instead. That's because Predef includes the following implicit conversions:"
   ]
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      "text/plain": [
       "\u001b[32mimport \u001b[39m\u001b[36mscala.language.implicitConversions\n",
       "\n",
       "\u001b[39m\n",
       "defined \u001b[32mfunction\u001b[39m \u001b[36mint2Integer\u001b[39m"
      ]
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     "execution_count": 2,
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    }
   ],
   "source": [
    "import scala.language.implicitConversions\n",
    "\n",
    "implicit def int2Integer(x: Int) =\n",
    "  java.lang.Integer.valueOf(x)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Because implicit conversions can have pitfalls if used indiscriminately the compiler warns when compiling the implicit conversion definition.\n",
    "\n",
    "To turn off the warnings take either of these actions:\n",
    "\n",
    "* Import `scala.language.implicitConversions` into the scope of the implicit conversion definition\n",
    "* Invoke the compiler with `-language:implicitConversions`\n",
    "\n",
    "No warning is emitted when the conversion is applied by the compiler.\n",
    "<p style=\"float: left;\"><a href=\"implicit-parameters.ipynb\" target=\"_blank\">Previous</a></p>\n",
    "<p style=\"float: right;\"><a href=\"polymorphic-methods.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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