8-Functions.ipynb

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   "source": [
    "# Table of Contents\n",
    " <p><div class=\"lev1 toc-item\"><a href=\"#Functions\" data-toc-modified-id=\"Functions-1\"><span class=\"toc-item-num\">1&nbsp;&nbsp;</span>Functions</a></div><div class=\"lev2 toc-item\"><a href=\"#関数の宣言\" data-toc-modified-id=\"関数の宣言-11\"><span class=\"toc-item-num\">1.1&nbsp;&nbsp;</span>関数の宣言</a></div><div class=\"lev2 toc-item\"><a href=\"#代入形式での関数宣言\" data-toc-modified-id=\"代入形式での関数宣言-12\"><span class=\"toc-item-num\">1.2&nbsp;&nbsp;</span>代入形式での関数宣言</a></div><div class=\"lev2 toc-item\"><a href=\"#無名関数\" data-toc-modified-id=\"無名関数-13\"><span class=\"toc-item-num\">1.3&nbsp;&nbsp;</span>無名関数</a></div><div class=\"lev2 toc-item\"><a href=\"#return\" data-toc-modified-id=\"return-14\"><span class=\"toc-item-num\">1.4&nbsp;&nbsp;</span>return</a></div><div class=\"lev2 toc-item\"><a href=\"#operatorを利用した関数\" data-toc-modified-id=\"operatorを利用した関数-15\"><span class=\"toc-item-num\">1.5&nbsp;&nbsp;</span>operatorを利用した関数</a></div>"
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   "metadata": {},
   "source": [
    "# Functions"
   ]
  },
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   "metadata": {},
   "source": [
    "## 関数の宣言"
   ]
  },
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    {
     "data": {
      "text/plain": [
       "say_name (generic function with 1 method)"
      ]
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   "source": [
    "# function～endで関数を定義する。\n",
    "# Pythonはコロンとインデントでfunctionのbodyを判定するが、juliaでは、function～endでやるみたい。\n",
    "function say_name(name)\n",
    "    println(\"$name\")\n",
    "end"
   ]
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   "outputs": [
    {
     "name": "stdout",
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     "text": [
      "banana\n"
     ]
    }
   ],
   "source": [
    "# 関数を宣言したら、以下のように使用できる。\n",
    "say_name(\"banana\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 代入形式での関数宣言"
   ]
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   "execution_count": 3,
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   "outputs": [
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     "data": {
      "text/plain": [
       "say_name_oneline (generic function with 1 method)"
      ]
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     "execution_count": 3,
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   ],
   "source": [
    "# 上で示した関数程度ならワンライナーで関数も宣言できる。\n",
    "say_name_oneline(name) = println(\"$name\")"
   ]
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   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "banana\n"
     ]
    }
   ],
   "source": [
    "# 使い方は同じ\n",
    "say_name_oneline(\"banana\")"
   ]
  },
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   "execution_count": 5,
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   "outputs": [
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     "data": {
      "text/plain": [
       "say_name_lines (generic function with 1 method)"
      ]
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   "source": [
    "# 以下みたいな感じで、複数行のやつもできる\n",
    "say_name_lines(name) = begin\n",
    "    output = name * \" : 複数行\"\n",
    "    println(output)\n",
    "end"
   ]
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     "text": [
      "banana : 複数行\n"
     ]
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   "source": [
    "say_name_lines(\"banana\")"
   ]
  },
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   "metadata": {},
   "source": [
    "## 無名関数"
   ]
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     "data": {
      "text/plain": [
       "(::#1) (generic function with 1 method)"
      ]
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     "execution_count": 7,
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   ],
   "source": [
    "# pythonでいうところのlambdaみたいなことができる\n",
    "say_name_anonymous = name -> println(\"$name\")"
   ]
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     "name": "stdout",
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     "text": [
      "banana\n"
     ]
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   "source": [
    "say_name_anonymous(\"banana\")"
   ]
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   "source": [
    "## return"
   ]
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   "outputs": [
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     "name": "stdout",
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     "text": [
      "15\n"
     ]
    }
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   "source": [
    "# juliaではdefaultで、一番最後に評価した値を返します。\n",
    "# そのため、return文を使わなくても値を返すことができます。\n",
    "\n",
    "function sample(x, y)\n",
    "    # returnを使っていない\n",
    "    x + y\n",
    "end\n",
    "\n",
    "value = sample(5, 10)\n",
    "# でも値は返ってくる\n",
    "println(value)"
   ]
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   "execution_count": 10,
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     "text": [
      "50\n"
     ]
    }
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   "source": [
    "# returnを使うとそこで強制的に値を返す\n",
    "function sample_return(x, y)\n",
    "    return x * y\n",
    "    x + y\n",
    "end\n",
    "\n",
    "value = sample_return(5, 10)\n",
    "\n",
    "# 掛け算した値が返ってくる\n",
    "println(value)"
   ]
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   "execution_count": 11,
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   "outputs": [
    {
     "data": {
      "text/plain": [
       "fizzbuzz (generic function with 1 method)"
      ]
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     "execution_count": 11,
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   "source": [
    "# 普通はもう少し入り組んだ処理を書くと思うので、returnを普通に使うと思います\n",
    "# returnで値を返すとそれ以降の処理をしなくなるので、便利です。\n",
    "function fizzbuzz(x)\n",
    "    if x % 3 == 0 && x % 5 == 0\n",
    "        return \"fizzbuzz\"\n",
    "    elseif x % 3 == 0\n",
    "        return \"fizz\"\n",
    "    elseif x % 5 == 0\n",
    "        return \"buzz\"\n",
    "    else\n",
    "        return \"\"\n",
    "    end\n",
    "end"
   ]
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    {
     "data": {
      "text/plain": [
       "\"fizzbuzz\""
      ]
     },
     "execution_count": 12,
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   ],
   "source": [
    "fizzbuzz(15)"
   ]
  },
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   "source": [
    "## operatorを利用した関数"
   ]
  },
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       "6"
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   "source": [
    "# こんなことができるんですね笑\n",
    "+(1, 2, 3)"
   ]
  },
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     "data": {
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       "24"
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     "execution_count": 14,
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   "source": [
    "# これはすなわち以下と同じです。\n",
    "1 + 2 + 3\n",
    "\n",
    "# juliaでは、ほとんどのoperatorが関数として特別なsytaxをサポートしているみたいです。\n",
    "# この書き方は斬新ですね笑\n",
    "*(1, 2, 3, 4)"
   ]
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     "data": {
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       "6"
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     "execution_count": 15,
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   "source": [
    "# つまり、以下と同じことをしているみたい\n",
    "f = +\n",
    "f(1,2,3)\n",
    "\n",
    "# 足し算とかの処理程度であれば、入力が可変にできますし、便利ですね。"
   ]
  }
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