{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Some과 Option\n",
    "\n",
    "* 기존 /\n",
    "a = 1 (값이 있음), a = null (값이 없음)\n",
    "\n",
    "* Option 사용 / \n",
    "a = Some(1) (값이 있음), a = None (값이 없음)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "\u001b[36ma\u001b[39m: \u001b[32mInt\u001b[39m = \u001b[32m1\u001b[39m"
      ]
     },
     "execution_count": 1,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "val a = 1"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "cmd1.sc:3: an expression of type Null is ineligible for implicit conversion\n",
      "val res1_1 = a = null\n",
      "                 ^"
     ]
    },
    {
     "ename": "",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "Compilation Failed"
     ]
    }
   ],
   "source": [
    "var a = 1\n",
    "// scala는 a에 null을 대입할 수 없음.\n",
    "a = null"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "\u001b[36ma\u001b[39m: \u001b[32mSome\u001b[39m[\u001b[32mInt\u001b[39m] = \u001b[33mSome\u001b[39m(\u001b[32m1\u001b[39m)\n",
       "\u001b[36mres1_1\u001b[39m: \u001b[32mOption\u001b[39m[\u001b[32mInt\u001b[39m] = \u001b[33mSome\u001b[39m(\u001b[32m2\u001b[39m)"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "val a = Some(1)\n",
    "// if(a.isEmpty) null else a.get + 1 안좋은 코드 예시\n",
    "a.map(_ + 1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "\u001b[36mres2\u001b[39m: \u001b[32mInt\u001b[39m = \u001b[32m1\u001b[39m"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a.getOrElse(-1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "\u001b[36ma\u001b[39m: \u001b[32mNone\u001b[39m.type = None"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "val a = None"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Functional Literal"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "\u001b[36mlist\u001b[39m: \u001b[32mList\u001b[39m[\u001b[32mInt\u001b[39m] = \u001b[33mList\u001b[39m(\u001b[32m1\u001b[39m, \u001b[32m2\u001b[39m, \u001b[32m3\u001b[39m, \u001b[32m4\u001b[39m)\n",
       "\u001b[36mres4_1\u001b[39m: \u001b[32mList\u001b[39m[\u001b[32mInt\u001b[39m] = \u001b[33mList\u001b[39m(\u001b[32m1\u001b[39m, \u001b[32m2\u001b[39m)\n",
       "\u001b[36mtestNumber1\u001b[39m: \u001b[32mInt\u001b[39m => \u001b[32mBoolean\u001b[39m = <function1>\n",
       "\u001b[36mres4_3\u001b[39m: \u001b[32mList\u001b[39m[\u001b[32mInt\u001b[39m] = \u001b[33mList\u001b[39m(\u001b[32m1\u001b[39m, \u001b[32m2\u001b[39m)\n",
       "\u001b[36mres4_4\u001b[39m: \u001b[32mList\u001b[39m[\u001b[32mInt\u001b[39m] = \u001b[33mList\u001b[39m(\u001b[32m1\u001b[39m, \u001b[32m2\u001b[39m)\n",
       "\u001b[36mres4_5\u001b[39m: \u001b[32mList\u001b[39m[\u001b[32mInt\u001b[39m] = \u001b[33mList\u001b[39m(\u001b[32m1\u001b[39m, \u001b[32m2\u001b[39m)\n",
       "defined \u001b[32mfunction\u001b[39m \u001b[36mtestNumber2\u001b[39m\n",
       "\u001b[36mres4_7\u001b[39m: \u001b[32mList\u001b[39m[\u001b[32mInt\u001b[39m] = \u001b[33mList\u001b[39m(\u001b[32m1\u001b[39m, \u001b[32m2\u001b[39m)\n",
       "\u001b[36mres4_8\u001b[39m: \u001b[32mList\u001b[39m[\u001b[32mInt\u001b[39m] = \u001b[33mList\u001b[39m(\u001b[32m1\u001b[39m, \u001b[32m2\u001b[39m)\n",
       "\u001b[36mres4_9\u001b[39m: \u001b[32mList\u001b[39m[\u001b[32mInt\u001b[39m] = \u001b[33mList\u001b[39m(\u001b[32m1\u001b[39m, \u001b[32m2\u001b[39m)\n",
       "\u001b[36mres4_10\u001b[39m: \u001b[32mList\u001b[39m[\u001b[32mInt\u001b[39m] = \u001b[33mList\u001b[39m(\u001b[32m1\u001b[39m, \u001b[32m2\u001b[39m)"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "val list = List(1, 2, 3, 4)\n",
    "list.filter((x: Int) => x < 3)\n",
    "val testNumber1 = (x: Int) => x < 3 // function as a 1st-class object! list.filter(testNumber1)\n",
    "list.filter((x) => x < 3) // target typing\n",
    "list.filter(x => x < 3)\n",
    "list.filter(_ < 3) // placeholder\n",
    "def testNumber2(x: Int) = x < 3 // function\n",
    "list.filter(x => testNumber2(x))\n",
    "list.filter(testNumber2(_))\n",
    "list.filter(testNumber2 _)\n",
    "list.filter(testNumber2)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Pattern Matching & Case Class\n",
    "• Java의 switch ~ case 와 비슷하지만, 훨씬 강력한 도구"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "\u001b[36ma\u001b[39m: \u001b[32mList\u001b[39m[(\u001b[32mInt\u001b[39m, (\u001b[32mInt\u001b[39m, \u001b[32mInt\u001b[39m))] = \u001b[33mList\u001b[39m((\u001b[32m1\u001b[39m, (\u001b[32m0\u001b[39m, \u001b[32m4\u001b[39m)), (\u001b[32m2\u001b[39m, (\u001b[32m0\u001b[39m, \u001b[32m5\u001b[39m)))"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "val a = List((1,(0,4)), (2,(0,5)))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "4\n",
      "5\n"
     ]
    }
   ],
   "source": [
    "a.map(_._2._2) foreach println // 튜플의 key의 right 원소를 뽑고 싶음. 보기 불편함."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "4\n",
      "5\n"
     ]
    }
   ],
   "source": [
    "a.map{case(key,(left,right)) => right} foreach println"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Implicit Conversion\n",
    "• 기능의 확장을 편하게 하고싶을때\n",
    "\n",
    "• 예상되는 타입으로 변환하는 함수를 정의해놓고, 자동으로 적용"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "defined \u001b[32mfunction\u001b[39m \u001b[36mstringToInt\u001b[39m\n",
       "defined \u001b[32mfunction\u001b[39m \u001b[36mprintNumber\u001b[39m"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "implicit def stringToInt(number: String): Int = { \n",
    "    number match {\n",
    "        case \"one\" => 1\n",
    "        case \"two\" => 2 \n",
    "    }\n",
    "}\n",
    "def printNumber(n: Int) = println(n)\n",
    "printNumber(\"one\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Implicit Conversion 활용 \n",
    "더 직관적이고 일관성 있는 코드를 만들 수 있다!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "\u001b[36mres9_0\u001b[39m: \u001b[32mjava\u001b[39m.\u001b[32mutil\u001b[39m.\u001b[32mDate\u001b[39m = Tue May 29 20:47:26 KST 2018\n",
       "\u001b[36mres9_1\u001b[39m: \u001b[32mjava\u001b[39m.\u001b[32mutil\u001b[39m.\u001b[32mDate\u001b[39m = Tue May 29 20:47:26 KST 2018\n",
       "defined \u001b[32mobject\u001b[39m \u001b[36mDateParser\u001b[39m\n",
       "\u001b[36mres9_3\u001b[39m: \u001b[32mjava\u001b[39m.\u001b[32mutil\u001b[39m.\u001b[32mDate\u001b[39m = Tue May 29 20:47:26 KST 2018\n",
       "defined \u001b[32mclass\u001b[39m \u001b[36mDateConverter\u001b[39m\n",
       "defined \u001b[32mfunction\u001b[39m \u001b[36mstring2DateConverter\u001b[39m\n",
       "\u001b[36mres9_6\u001b[39m: \u001b[32mjava\u001b[39m.\u001b[32mutil\u001b[39m.\u001b[32mDate\u001b[39m = Tue May 29 20:47:26 KST 2018"
      ]
     },
     "execution_count": 10,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "DateParser.parse(\"2017-07-29\") // java style\n",
    "\"2017-07-29\".toDateTime // better solution using implicit conversion\n",
    "object DateParser {\n",
    "  def parse(dateString :String) = new java.util.Date\n",
    "}\n",
    "DateParser.parse(\"2017-07-29\")\n",
    "class DateConverter(val s: String) {\n",
    "  def toDateTime = DateParser.parse(s)\n",
    "}\n",
    "implicit def string2DateConverter(s: String) = new DateConverter(s)\n",
    "\"2017-07-29\".toDateTime"
   ]
  }
 ],
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   "name": "scala"
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