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   "source": [
    "<p style=\"float: left;\"><a href=\"variances.ipynb\" target=\"_blank\">Previous</a></p>\n",
    "<p style=\"float: right;\"><a href=\"lower-type-bounds.ipynb\" target=\"_blank\">Next</a></p>\n",
    "<p style=\"text-align:center;\">Tour of Scala</p>\n",
    "<div style=\"clear: both;\"></div>\n",
    "\n",
    "# Upper Type Bounds\n",
    "\n",
    "In Scala, [type parameters](generic-classes.ipynb) and [abstract types](abstract-types.ipynb) may be constrained by a type bound. Such type bounds limit the concrete values of the type variables and possibly reveal more information about the members of such types. An _upper type bound_ `T <: A` declares that type variable `T` refers to a subtype of type `A`.\n",
    "Here is an example that demonstrates upper type bound for a type parameter of class `PetContainer`:"
   ]
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       "defined \u001b[32mclass\u001b[39m \u001b[36mAnimal\u001b[39m\n",
       "defined \u001b[32mclass\u001b[39m \u001b[36mPet\u001b[39m\n",
       "defined \u001b[32mclass\u001b[39m \u001b[36mCat\u001b[39m\n",
       "defined \u001b[32mclass\u001b[39m \u001b[36mDog\u001b[39m\n",
       "defined \u001b[32mclass\u001b[39m \u001b[36mLion\u001b[39m\n",
       "defined \u001b[32mclass\u001b[39m \u001b[36mPetContainer\u001b[39m\n",
       "\u001b[36mdogContainer\u001b[39m: \u001b[32mPetContainer\u001b[39m[\u001b[32mDog\u001b[39m] = ammonite.$sess.cmd0$Helper$PetContainer@5ce7ef5d\n",
       "\u001b[36mcatContainer\u001b[39m: \u001b[32mPetContainer\u001b[39m[\u001b[32mCat\u001b[39m] = ammonite.$sess.cmd0$Helper$PetContainer@5caf67b8"
      ]
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   "source": [
    "abstract class Animal {\n",
    " def name: String\n",
    "}\n",
    "\n",
    "abstract class Pet extends Animal {}\n",
    "\n",
    "class Cat extends Pet {\n",
    "  override def name: String = \"Cat\"\n",
    "}\n",
    "\n",
    "class Dog extends Pet {\n",
    "  override def name: String = \"Dog\"\n",
    "}\n",
    "\n",
    "class Lion extends Animal {\n",
    "  override def name: String = \"Lion\"\n",
    "}\n",
    "\n",
    "class PetContainer[P <: Pet](p: P) {\n",
    "  def pet: P = p\n",
    "}\n",
    "\n",
    "val dogContainer = new PetContainer[Dog](new Dog)\n",
    "val catContainer = new PetContainer[Cat](new Cat)"
   ]
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     "text": [
      "cmd1.sc:104: type arguments [cmd1.this.cmd0.Lion] do not conform to class PetContainer's type parameter bounds [P <: Helper.this.Pet]\n",
      "val lionContainer = new PetContainer[Lion](new Lion)\n",
      "    ^cmd1.sc:1: type arguments [cmd1.this.cmd0.Lion] do not conform to class PetContainer's type parameter bounds [P <: Helper.this.Pet]\n",
      "val lionContainer = new PetContainer[Lion](new Lion)\n",
      "                        ^cmd1.sc:8: type arguments [cmd1.this.cmd0.Lion] do not conform to class PetContainer's type parameter bounds [P <: Helper.this.Pet]\n",
      "            .print(lionContainer, \"lionContainer\", _root_.scala.None)\n",
      "             ^cmd1.sc:8: type arguments [cmd1.this.cmd0.Lion] do not conform to class PetContainer's type parameter bounds [P <: Helper.this.Pet]\n",
      "            .print(lionContainer, \"lionContainer\", _root_.scala.None)\n",
      "                  ^Compilation Failed"
     ]
    },
    {
     "ename": "",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "Compilation Failed"
     ]
    }
   ],
   "source": [
    "// this would not compile\n",
    "val lionContainer = new PetContainer[Lion](new Lion)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The `class PetContainer` take a type parameter `P` which must be a subtype of `Pet`. `Dog` and `Cat` are subtypes of `Pet` so we can create a new `PetContainer[Dog]` and `PetContainer[Cat]`. However, if we tried to create a `PetContainer[Lion]`, we would get the following Error:\n",
    "\n",
    "`type arguments [Lion] do not conform to class PetContainer's type parameter bounds [P <: Pet]`\n",
    "\n",
    "This is because `Lion` is not a subtype of `Pet`.\n",
    "<p style=\"float: left;\"><a href=\"variances.ipynb\" target=\"_blank\">Previous</a></p>\n",
    "<p style=\"float: right;\"><a href=\"lower-type-bounds.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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