Jekyll에 Giscus로 comment 기능 추가

Jekyll에 Giscus를 추가하는 방법은 간단하며, 아래 단계를 따르면 됩니다.

Giscus란?

Giscus는 GitHub Discussions를 기반으로 한 오픈소스 댓글 시스템입니다. 기존의 Disqus나 utterances와 비교하여 여러 장점이 있습니다:

비교 항목	Giscus	Disqus	utterances
가격	무료	무료(광고)/유료	무료
데이터 저장	GitHub Discussions	Disqus 서버	GitHub Issues
광고	없음	무료 플랜에 있음	없음
반응(리액션)	지원	지원	미지원
댓글 스레딩	지원	지원	미지원
다크 모드	지원	제한적	지원
데이터 소유권	사용자	Disqus	사용자

Giscus는 댓글이 GitHub Discussions에 저장되므로 데이터의 소유권이 사용자에게 있으며, 언제든지 마이그레이션이 가능합니다.

사전 준비

Giscus를 사용하기 전에 아래 조건을 충족해야 합니다:

공개 GitHub 저장소: 댓글이 저장될 저장소가 공개(public)여야 합니다.
Discussions 기능 활성화: 저장소 Settings → General → Features에서 Discussions를 체크합니다.
Giscus 앱 설치: giscus app을 저장소에 설치합니다.

1. Giscus 설정하기

Giscus 공식 웹사이트에 접속합니다.
아래 정보를 입력합니다:
- Repository: 댓글을 저장할 GitHub 저장소 선택 (예: your-username/your-repo)
- Discussion Category: Giscus에서 사용할 Discussion 카테고리 선택 (Announcements 추천)
- Mapping: 페이지와 댓글을 연결하는 방식 선택 (예: pathname)
- Reaction: 사용자가 댓글에 반응할 수 있도록 활성화할지 여부 설정
- Theme: Giscus 위젯의 테마 설정 (예: light, dark, preferred_color_scheme)
- 기타 필요 옵션 설정 후 Code Snippet 복사.

Mapping 옵션 설명

pathname: URL 경로로 매핑. 가장 일반적이고 안정적인 방식입니다.
URL: 전체 URL로 매핑. 도메인 변경 시 댓글이 분리될 수 있습니다.
title: 페이지 제목으로 매핑. 제목 변경 시 댓글이 분리될 수 있습니다.
og:title: Open Graph 제목으로 매핑.
특정 용어: 직접 지정한 용어로 매핑.

대부분의 경우 pathname 방식을 권장합니다.

2. Jekyll 테마 수정

Giscus 스크립트를 Jekyll 블로그의 적절한 위치에 추가합니다.

(1) _layouts 파일 수정

Giscus를 추가할 위치에 따라 주로 post.html 또는 default.html 파일을 수정합니다.

예: _layouts/post.html

<article>
  <article class="post h-entry" itemscope itemtype="http://schema.org/BlogPosting">

  <header class="post-header">
    <h1 class="post-title p-name" itemprop="name headline">Kotlin 클래스와 객체: Class, Data Class, Sealed Class, Object</h1>
    <p class="post-meta">
      <time class="dt-published" datetime="2025-01-25T04:35:00+00:00" itemprop="datePublished">Jan 25, 2025
      </time></p><div class="post-categories"><a href="/Programming/" class="post-category-badge">Programming</a><span class="category-separator">›</span><a href="/Kotlin/" class="post-category-badge">Kotlin</a></div></header><img src="/assets/images/posts/thumbnails/2025-12-28-kotlin-classes-objects.png" alt="Kotlin 클래스와 객체: Class, Data Class, Sealed Class, Object" class="post-thumbnail" itemprop="image"><div class="post-content e-content" itemprop="articleBody">
    <p>Kotlin은 객체 지향 프로그래밍을 위한 풍부한 기능을 제공합니다. 이 포스트에서는 다양한 클래스 유형과 객체에 대해 알아보겠습니다.</p>

<h2 id="클래스-선언">클래스 선언</h2>

<h3 id="기본-클래스">기본 클래스</h3>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c1">// 파라미터 없는 경우</span>
<span class="kd">class</span> <span class="nc">Greeter</span><span class="p">()</span> <span class="p">{</span>
    <span class="k">fun</span> <span class="nf">greet</span><span class="p">()</span> <span class="p">{</span>
    <span class="p">}</span>
<span class="p">}</span>

<span class="c1">// read only, mutable 파라미터</span>
<span class="kd">class</span> <span class="nc">Greeter</span><span class="p">(</span><span class="kd">val</span> <span class="py">name</span><span class="p">:</span> <span class="nc">String</span><span class="p">,</span> <span class="kd">var</span> <span class="py">age</span><span class="p">:</span> <span class="nc">Int</span><span class="p">)</span> <span class="p">{</span>
    <span class="k">fun</span> <span class="nf">greet</span><span class="p">()</span> <span class="p">{</span>
        <span class="nf">println</span><span class="p">(</span><span class="s">"Hello, ${name}"</span><span class="p">)</span>
    <span class="p">}</span>
<span class="p">}</span>

<span class="c1">// body가 없는 경우 중괄호 생략 가능</span>
<span class="kd">class</span> <span class="nc">A</span><span class="p">(</span><span class="n">a</span><span class="p">:</span> <span class="nc">Int</span><span class="p">)</span>

<span class="c1">// visibility modifier와 annotation이 있는 생성자</span>
<span class="kd">class</span> <span class="nc">Customer</span> <span class="k">public</span> <span class="nd">@Inject</span> <span class="k">constructor</span><span class="p">(</span><span class="n">name</span><span class="p">:</span> <span class="nc">String</span><span class="p">)</span> <span class="p">{</span> <span class="o">..</span><span class="p">.</span> <span class="p">}</span>
</code></pre></div></div>

<h3 id="상속">상속</h3>

<p>기본적으로 Kotlin의 모든 클래스는 <code class="language-plaintext highlighter-rouge">final</code>입니다. 상속을 허용하려면 <code class="language-plaintext highlighter-rouge">open</code> 키워드를 사용해야 합니다.</p>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">open</span> <span class="kd">class</span> <span class="nc">A</span>  <span class="c1">// 상속 가능</span>

<span class="kd">class</span> <span class="nc">B</span> <span class="p">:</span> <span class="nc">A</span><span class="p">()</span> <span class="p">{</span>
    <span class="k">override</span> <span class="k">fun</span> <span class="nf">foo</span><span class="p">(</span><span class="n">i</span><span class="p">:</span> <span class="nc">Int</span><span class="p">)</span> <span class="p">{</span> <span class="o">..</span><span class="p">.</span> <span class="p">}</span>
<span class="p">}</span>

<span class="c1">// 파라미터가 있는 클래스 상속</span>
<span class="kd">class</span> <span class="nc">Rectangle</span><span class="p">(</span>
    <span class="kd">var</span> <span class="py">height</span><span class="p">:</span> <span class="nc">Double</span><span class="p">,</span>
    <span class="kd">var</span> <span class="py">length</span><span class="p">:</span> <span class="nc">Double</span>
<span class="p">)</span> <span class="p">:</span> <span class="nc">Shape</span><span class="p">(</span><span class="nf">listOf</span><span class="p">(</span><span class="n">height</span><span class="p">,</span> <span class="n">length</span><span class="p">,</span> <span class="n">height</span><span class="p">,</span> <span class="n">length</span><span class="p">))</span> <span class="p">{</span> <span class="o">..</span><span class="p">.</span> <span class="p">}</span>
</code></pre></div></div>

<h3 id="추상-클래스">추상 클래스</h3>

<p>추상 클래스는 <code class="language-plaintext highlighter-rouge">open</code> 키워드가 필요 없습니다.</p>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">abstract</span> <span class="kd">class</span> <span class="nc">Shape</span><span class="p">(</span><span class="kd">val</span> <span class="py">sides</span><span class="p">:</span> <span class="nc">List</span><span class="p">&lt;</span><span class="nc">Double</span><span class="p">&gt;)</span> <span class="p">{</span>
    <span class="kd">val</span> <span class="py">perimeter</span><span class="p">:</span> <span class="nc">Double</span> <span class="k">get</span><span class="p">()</span> <span class="p">=</span> <span class="n">sides</span><span class="p">.</span><span class="nf">sum</span><span class="p">()</span>
    <span class="k">abstract</span> <span class="k">fun</span> <span class="nf">calculateArea</span><span class="p">():</span> <span class="nc">Double</span>
<span class="p">}</span>

<span class="c1">// 비추상 멤버를 추상으로 오버라이드</span>
<span class="k">open</span> <span class="kd">class</span> <span class="nc">Base</span> <span class="p">{</span>
    <span class="k">open</span> <span class="k">fun</span> <span class="nf">f</span><span class="p">()</span> <span class="p">{}</span>
<span class="p">}</span>

<span class="k">abstract</span> <span class="kd">class</span> <span class="nc">Derived</span> <span class="p">:</span> <span class="nc">Base</span><span class="p">()</span> <span class="p">{</span>
    <span class="k">override</span> <span class="k">abstract</span> <span class="k">fun</span> <span class="nf">f</span><span class="p">()</span>
<span class="p">}</span>
</code></pre></div></div>

<h3 id="생성자">생성자</h3>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c1">// Secondary constructor</span>
<span class="kd">class</span> <span class="nc">Person</span> <span class="p">{</span>
    <span class="k">constructor</span><span class="p">(</span><span class="n">parent</span><span class="p">:</span> <span class="nc">Person</span><span class="p">)</span> <span class="p">{</span>
        <span class="n">parent</span><span class="p">.</span><span class="n">children</span><span class="p">.</span><span class="nf">add</span><span class="p">(</span><span class="k">this</span><span class="p">)</span>
    <span class="p">}</span>
<span class="p">}</span>

<span class="c1">// Primary constructor가 있는 경우 delegation 필수</span>
<span class="kd">class</span> <span class="nc">Person</span><span class="p">(</span><span class="kd">val</span> <span class="py">name</span><span class="p">:</span> <span class="nc">String</span><span class="p">)</span> <span class="p">{</span>
    <span class="k">constructor</span><span class="p">(</span><span class="n">name</span><span class="p">:</span> <span class="nc">String</span><span class="p">,</span> <span class="n">parent</span><span class="p">:</span> <span class="nc">Person</span><span class="p">)</span> <span class="p">:</span> <span class="k">this</span><span class="p">(</span><span class="n">name</span><span class="p">)</span> <span class="p">{</span>
        <span class="n">parent</span><span class="p">.</span><span class="n">children</span><span class="p">.</span><span class="nf">add</span><span class="p">(</span><span class="k">this</span><span class="p">)</span>
    <span class="p">}</span>
<span class="p">}</span>

<span class="c1">// super 생성자 호출</span>
<span class="kd">class</span> <span class="nc">MyView</span> <span class="p">:</span> <span class="nc">View</span> <span class="p">{</span>
    <span class="k">constructor</span><span class="p">(</span><span class="n">ctx</span><span class="p">:</span> <span class="nc">Context</span><span class="p">)</span> <span class="p">:</span> <span class="k">super</span><span class="p">(</span><span class="n">ctx</span><span class="p">)</span>
    <span class="k">constructor</span><span class="p">(</span><span class="n">ctx</span><span class="p">:</span> <span class="nc">Context</span><span class="p">,</span> <span class="n">attrs</span><span class="p">:</span> <span class="nc">AttributeSet</span><span class="p">)</span> <span class="p">:</span> <span class="k">super</span><span class="p">(</span><span class="n">ctx</span><span class="p">,</span> <span class="n">attrs</span><span class="p">)</span>
<span class="p">}</span>

<span class="c1">// private constructor</span>
<span class="kd">class</span> <span class="nc">C</span> <span class="k">private</span> <span class="k">constructor</span><span class="p">(</span><span class="n">a</span><span class="p">:</span> <span class="nc">Int</span><span class="p">)</span> <span class="p">{</span> <span class="o">..</span><span class="p">.</span> <span class="p">}</span>

<span class="c1">// private property in constructor</span>
<span class="kd">class</span> <span class="nc">ParameterizedClass</span><span class="p">&lt;</span><span class="nc">A</span><span class="p">&gt;(</span><span class="k">private</span> <span class="kd">val</span> <span class="py">value</span><span class="p">:</span> <span class="nc">A</span><span class="p">)</span> <span class="p">{</span>
    <span class="k">fun</span> <span class="nf">getValue</span><span class="p">():</span> <span class="nc">A</span> <span class="p">=</span> <span class="n">value</span>
<span class="p">}</span>
</code></pre></div></div>

<h3 id="초기화-블록">초기화 블록</h3>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">class</span> <span class="nc">Customer</span><span class="p">(</span><span class="n">name</span><span class="p">:</span> <span class="nc">String</span><span class="p">)</span> <span class="p">{</span>
    <span class="nf">init</span> <span class="p">{</span>
        <span class="n">logger</span><span class="p">.</span><span class="nf">info</span><span class="p">(</span><span class="s">"Customer initialized with value ${name}"</span><span class="p">)</span>
    <span class="p">}</span>

    <span class="kd">val</span> <span class="py">customerKey</span> <span class="p">=</span> <span class="n">name</span><span class="p">.</span><span class="nf">toUpperCase</span><span class="p">()</span>
<span class="p">}</span>
</code></pre></div></div>

<h3 id="중첩-클래스">중첩 클래스</h3>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c1">// Static nested class (기본)</span>
<span class="kd">class</span> <span class="nc">Outer</span> <span class="p">{</span>
    <span class="k">private</span> <span class="kd">val</span> <span class="py">bar</span><span class="p">:</span> <span class="nc">Int</span> <span class="p">=</span> <span class="mi">1</span>
    <span class="kd">class</span> <span class="nc">Nested</span> <span class="p">{</span>
        <span class="k">fun</span> <span class="nf">foo</span><span class="p">()</span> <span class="p">=</span> <span class="mi">2</span>
    <span class="p">}</span>
<span class="p">}</span>
<span class="kd">val</span> <span class="py">demo</span> <span class="p">=</span> <span class="nc">Outer</span><span class="p">.</span><span class="nc">Nested</span><span class="p">().</span><span class="nf">foo</span><span class="p">()</span>  <span class="c1">// == 2</span>

<span class="c1">// Inner class (외부 클래스 참조 가능)</span>
<span class="kd">class</span> <span class="nc">Outer</span> <span class="p">{</span>
    <span class="k">private</span> <span class="kd">val</span> <span class="py">bar</span><span class="p">:</span> <span class="nc">Int</span> <span class="p">=</span> <span class="mi">1</span>
    <span class="k">inner</span> <span class="kd">class</span> <span class="nc">Inner</span> <span class="p">{</span>
        <span class="k">fun</span> <span class="nf">foo</span><span class="p">()</span> <span class="p">=</span> <span class="n">bar</span>
    <span class="p">}</span>
<span class="p">}</span>
<span class="kd">val</span> <span class="py">demo</span> <span class="p">=</span> <span class="nc">Outer</span><span class="p">().</span><span class="nc">Inner</span><span class="p">().</span><span class="nf">foo</span><span class="p">()</span>  <span class="c1">// == 1</span>
</code></pre></div></div>

<h3 id="메서드-오버라이딩">메서드 오버라이딩</h3>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">open</span> <span class="kd">class</span> <span class="nc">Base</span> <span class="p">{</span>
    <span class="k">open</span> <span class="k">fun</span> <span class="nf">v</span><span class="p">()</span> <span class="p">{}</span>
    <span class="k">fun</span> <span class="nf">nv</span><span class="p">()</span> <span class="p">{}</span>  <span class="c1">// final by default</span>
<span class="p">}</span>

<span class="kd">class</span> <span class="nc">Derived</span><span class="p">()</span> <span class="p">:</span> <span class="nc">Base</span><span class="p">()</span> <span class="p">{</span>
    <span class="k">override</span> <span class="k">fun</span> <span class="nf">v</span><span class="p">()</span> <span class="p">{}</span>

    <span class="c1">// 추가 오버라이드 방지</span>
    <span class="k">final</span> <span class="k">override</span> <span class="k">fun</span> <span class="nf">v</span><span class="p">()</span> <span class="p">{}</span>
<span class="p">}</span>
</code></pre></div></div>

<h3 id="다중-상속에서의-충돌-해결">다중 상속에서의 충돌 해결</h3>

<p>인터페이스와 클래스에서 같은 시그니처의 메서드가 있을 경우:</p>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">open</span> <span class="kd">class</span> <span class="nc">A</span> <span class="p">{</span>
    <span class="k">open</span> <span class="k">fun</span> <span class="nf">f</span><span class="p">()</span> <span class="p">{</span> <span class="nf">print</span><span class="p">(</span><span class="s">"A"</span><span class="p">)</span> <span class="p">}</span>
    <span class="k">fun</span> <span class="nf">a</span><span class="p">()</span> <span class="p">{</span> <span class="nf">print</span><span class="p">(</span><span class="s">"a"</span><span class="p">)</span> <span class="p">}</span>
<span class="p">}</span>

<span class="kd">interface</span> <span class="nc">B</span> <span class="p">{</span>
    <span class="k">fun</span> <span class="nf">f</span><span class="p">()</span> <span class="p">{</span> <span class="nf">print</span><span class="p">(</span><span class="s">"B"</span><span class="p">)</span> <span class="p">}</span>  <span class="c1">// interface members are 'open' by default</span>
    <span class="k">fun</span> <span class="nf">b</span><span class="p">()</span> <span class="p">{</span> <span class="nf">print</span><span class="p">(</span><span class="s">"b"</span><span class="p">)</span> <span class="p">}</span>
<span class="p">}</span>

<span class="kd">class</span> <span class="nc">C</span><span class="p">()</span> <span class="p">:</span> <span class="nc">A</span><span class="p">(),</span> <span class="nc">B</span> <span class="p">{</span>
    <span class="c1">// 컴파일러가 f() 오버라이드를 요구함</span>
    <span class="k">override</span> <span class="k">fun</span> <span class="nf">f</span><span class="p">()</span> <span class="p">{</span>
        <span class="k">super</span><span class="p">&lt;</span><span class="nc">A</span><span class="p">&gt;.</span><span class="nf">f</span><span class="p">()</span>  <span class="c1">// A.f() 호출</span>
        <span class="k">super</span><span class="p">&lt;</span><span class="nc">B</span><span class="p">&gt;.</span><span class="nf">f</span><span class="p">()</span>  <span class="c1">// B.f() 호출</span>
    <span class="p">}</span>
<span class="p">}</span>
</code></pre></div></div>

<h3 id="프로퍼티-오버라이딩">프로퍼티 오버라이딩</h3>

<p>Kotlin에서는 프로퍼티도 오버라이드할 수 있습니다. <code class="language-plaintext highlighter-rouge">val</code>을 <code class="language-plaintext highlighter-rouge">var</code>로 오버라이드할 수 있지만, 그 반대는 불가능합니다.</p>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">open</span> <span class="kd">class</span> <span class="nc">Foo</span> <span class="p">{</span>
    <span class="k">open</span> <span class="kd">val</span> <span class="py">x</span><span class="p">:</span> <span class="nc">Int</span> <span class="k">get</span><span class="p">()</span> <span class="p">{</span> <span class="o">..</span><span class="p">.</span> <span class="p">}</span>
<span class="p">}</span>

<span class="kd">class</span> <span class="nc">Bar1</span> <span class="p">:</span> <span class="nc">Foo</span><span class="p">()</span> <span class="p">{</span>
    <span class="k">override</span> <span class="kd">var</span> <span class="py">x</span><span class="p">:</span> <span class="nc">Int</span> <span class="p">=</span> <span class="o">..</span><span class="p">.</span>  <span class="c1">// val -&gt; var 가능</span>
<span class="p">}</span>

<span class="c1">// Primary constructor에서 오버라이드</span>
<span class="kd">interface</span> <span class="nc">Foo</span> <span class="p">{</span>
    <span class="kd">val</span> <span class="py">count</span><span class="p">:</span> <span class="nc">Int</span>
<span class="p">}</span>

<span class="kd">class</span> <span class="nc">Bar1</span><span class="p">(</span><span class="k">override</span> <span class="kd">val</span> <span class="py">count</span><span class="p">:</span> <span class="nc">Int</span><span class="p">)</span> <span class="p">:</span> <span class="nc">Foo</span>
</code></pre></div></div>

<h3 id="this와-super-레이블">this와 super 레이블</h3>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">class</span> <span class="nc">A</span> <span class="p">{</span>
    <span class="k">inner</span> <span class="kd">class</span> <span class="nc">B</span> <span class="p">{</span>
        <span class="k">fun</span> <span class="nc">Int</span><span class="p">.</span><span class="nf">foo</span><span class="p">()</span> <span class="p">{</span>
            <span class="kd">val</span> <span class="py">a</span> <span class="p">=</span> <span class="k">this</span><span class="nd">@A</span>  <span class="c1">// A's this</span>
            <span class="kd">val</span> <span class="py">b</span> <span class="p">=</span> <span class="k">this</span><span class="nd">@B</span>  <span class="c1">// B's this</span>
            <span class="kd">val</span> <span class="py">c</span> <span class="p">=</span> <span class="k">this</span>    <span class="c1">// foo()'s receiver, an Int</span>
        <span class="p">}</span>
    <span class="p">}</span>
<span class="p">}</span>

<span class="kd">class</span> <span class="nc">Bar</span> <span class="p">:</span> <span class="nc">Foo</span><span class="p">()</span> <span class="p">{</span>
    <span class="k">override</span> <span class="k">fun</span> <span class="nf">f</span><span class="p">()</span> <span class="p">{</span> <span class="cm">/* ... */</span> <span class="p">}</span>

    <span class="k">inner</span> <span class="kd">class</span> <span class="nc">Baz</span> <span class="p">{</span>
        <span class="k">fun</span> <span class="nf">g</span><span class="p">()</span> <span class="p">{</span>
            <span class="k">super</span><span class="nd">@Bar</span><span class="p">.</span><span class="nf">f</span><span class="p">()</span>  <span class="c1">// Foo의 f() 호출</span>
        <span class="p">}</span>
    <span class="p">}</span>
<span class="p">}</span>
</code></pre></div></div>

<h2 id="인터페이스">인터페이스</h2>

<h3 id="선언과-구현">선언과 구현</h3>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">interface</span> <span class="nc">RectangleProperties</span> <span class="p">{</span>
    <span class="kd">val</span> <span class="py">isSquare</span><span class="p">:</span> <span class="nc">Boolean</span>
<span class="p">}</span>

<span class="c1">// 메서드 기본 구현 가능</span>
<span class="kd">interface</span> <span class="nc">B</span> <span class="p">{</span>
    <span class="k">fun</span> <span class="nf">f</span><span class="p">()</span> <span class="p">{</span> <span class="nf">print</span><span class="p">(</span><span class="s">"B"</span><span class="p">)</span> <span class="p">}</span>
    <span class="k">fun</span> <span class="nf">b</span><span class="p">()</span> <span class="p">{</span> <span class="nf">print</span><span class="p">(</span><span class="s">"b"</span><span class="p">)</span> <span class="p">}</span>
<span class="p">}</span>

<span class="c1">// 구현</span>
<span class="kd">class</span> <span class="nc">Rectangle</span> <span class="p">:</span> <span class="nc">Shape</span><span class="p">(),</span> <span class="nc">RectangleProperties</span> <span class="p">{</span>
    <span class="k">override</span> <span class="kd">val</span> <span class="py">isSquare</span><span class="p">:</span> <span class="nc">Boolean</span> <span class="k">get</span><span class="p">()</span> <span class="p">=</span> <span class="n">length</span> <span class="p">==</span> <span class="n">height</span>
<span class="p">}</span>
</code></pre></div></div>

<h2 id="data-class">Data Class</h2>

<p>Data class는 데이터를 보관하기 위한 클래스로, 다음 함수들을 자동 생성합니다:</p>
<ul>
  <li><code class="language-plaintext highlighter-rouge">equals()</code> / <code class="language-plaintext highlighter-rouge">hashCode()</code></li>
  <li><code class="language-plaintext highlighter-rouge">toString()</code> - “User(name=John, age=42)” 형식</li>
  <li><code class="language-plaintext highlighter-rouge">componentN()</code> 함수들</li>
  <li><code class="language-plaintext highlighter-rouge">copy()</code> 함수</li>
</ul>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">data class</span> <span class="nc">User</span><span class="p">(</span><span class="kd">val</span> <span class="py">name</span><span class="p">:</span> <span class="nc">String</span><span class="p">,</span> <span class="kd">val</span> <span class="py">age</span><span class="p">:</span> <span class="nc">Int</span><span class="p">)</span>

<span class="c1">// copy 사용</span>
<span class="kd">val</span> <span class="py">jack</span> <span class="p">=</span> <span class="nc">User</span><span class="p">(</span><span class="n">name</span> <span class="p">=</span> <span class="s">"Jack"</span><span class="p">,</span> <span class="n">age</span> <span class="p">=</span> <span class="mi">1</span><span class="p">)</span>
<span class="kd">val</span> <span class="py">olderJack</span> <span class="p">=</span> <span class="n">jack</span><span class="p">.</span><span class="nf">copy</span><span class="p">(</span><span class="n">age</span> <span class="p">=</span> <span class="mi">2</span><span class="p">)</span>
</code></pre></div></div>

<h3 id="destructuring-declarations">Destructuring Declarations</h3>

<p><code class="language-plaintext highlighter-rouge">componentN()</code> 함수가 있는 클래스에서 사용 가능합니다.</p>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">val</span> <span class="p">(</span><span class="py">name</span><span class="p">,</span> <span class="py">age</span><span class="p">)</span> <span class="p">=</span> <span class="n">person</span>
<span class="c1">// 아래와 동일</span>
<span class="kd">val</span> <span class="py">name</span> <span class="p">=</span> <span class="n">person</span><span class="p">.</span><span class="nf">component1</span><span class="p">()</span>
<span class="kd">val</span> <span class="py">age</span> <span class="p">=</span> <span class="n">person</span><span class="p">.</span><span class="nf">component2</span><span class="p">()</span>

<span class="c1">// for 문에서</span>
<span class="k">for</span> <span class="p">((</span><span class="n">a</span><span class="p">,</span> <span class="n">b</span><span class="p">)</span> <span class="k">in</span> <span class="n">collection</span><span class="p">)</span> <span class="p">{</span> <span class="o">..</span><span class="p">.</span> <span class="p">}</span>
<span class="k">for</span> <span class="p">((</span><span class="n">key</span><span class="p">,</span> <span class="n">value</span><span class="p">)</span> <span class="k">in</span> <span class="n">map</span><span class="p">)</span> <span class="p">{</span> <span class="o">..</span><span class="p">.</span> <span class="p">}</span>

<span class="c1">// 사용하지 않는 변수</span>
<span class="kd">val</span> <span class="p">(</span><span class="py">_</span><span class="p">,</span> <span class="py">status</span><span class="p">)</span> <span class="p">=</span> <span class="nf">getResult</span><span class="p">()</span>
</code></pre></div></div>

<h3 id="여러-값-반환하기">여러 값 반환하기</h3>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">data class</span> <span class="nc">Result</span><span class="p">(</span><span class="kd">val</span> <span class="py">result</span><span class="p">:</span> <span class="nc">Int</span><span class="p">,</span> <span class="kd">val</span> <span class="py">status</span><span class="p">:</span> <span class="nc">Status</span><span class="p">)</span>

<span class="k">fun</span> <span class="nf">function</span><span class="p">(</span><span class="o">..</span><span class="p">.):</span> <span class="nc">Result</span> <span class="p">{</span>
    <span class="c1">// computations</span>
    <span class="k">return</span> <span class="nc">Result</span><span class="p">(</span><span class="n">result</span><span class="p">,</span> <span class="n">status</span><span class="p">)</span>
<span class="p">}</span>

<span class="kd">val</span> <span class="p">(</span><span class="py">result</span><span class="p">,</span> <span class="py">status</span><span class="p">)</span> <span class="p">=</span> <span class="nf">function</span><span class="p">(</span><span class="o">..</span><span class="p">.)</span>
</code></pre></div></div>

<h2 id="sealed-class">Sealed Class</h2>

<p>Sealed class는 같은 파일 내에서만 상속이 가능합니다. 이를 통해 제한된 클래스 계층을 정의할 수 있습니다.</p>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">sealed</span> <span class="kd">class</span> <span class="nc">Expr</span>
<span class="kd">data class</span> <span class="nc">Const</span><span class="p">(</span><span class="kd">val</span> <span class="py">number</span><span class="p">:</span> <span class="nc">Double</span><span class="p">)</span> <span class="p">:</span> <span class="nc">Expr</span><span class="p">()</span>
<span class="kd">data class</span> <span class="nc">Sum</span><span class="p">(</span><span class="kd">val</span> <span class="py">e1</span><span class="p">:</span> <span class="nc">Expr</span><span class="p">,</span> <span class="kd">val</span> <span class="py">e2</span><span class="p">:</span> <span class="nc">Expr</span><span class="p">)</span> <span class="p">:</span> <span class="nc">Expr</span><span class="p">()</span>
<span class="kd">object</span> <span class="nc">NotANumber</span> <span class="p">:</span> <span class="nc">Expr</span><span class="p">()</span>
</code></pre></div></div>

<h3 id="when과-함께-사용">when과 함께 사용</h3>

<p>Sealed class의 모든 하위 클래스가 처리되면 <code class="language-plaintext highlighter-rouge">else</code> 절이 필요 없습니다.</p>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">fun</span> <span class="nf">eval</span><span class="p">(</span><span class="n">expr</span><span class="p">:</span> <span class="nc">Expr</span><span class="p">):</span> <span class="nc">Double</span> <span class="p">=</span> <span class="k">when</span><span class="p">(</span><span class="n">expr</span><span class="p">)</span> <span class="p">{</span>
    <span class="k">is</span> <span class="nc">Const</span> <span class="p">-&gt;</span> <span class="n">expr</span><span class="p">.</span><span class="n">number</span>
    <span class="k">is</span> <span class="nc">Sum</span> <span class="p">-&gt;</span> <span class="nf">eval</span><span class="p">(</span><span class="n">expr</span><span class="p">.</span><span class="n">e1</span><span class="p">)</span> <span class="p">+</span> <span class="nf">eval</span><span class="p">(</span><span class="n">expr</span><span class="p">.</span><span class="n">e2</span><span class="p">)</span>
    <span class="nc">NotANumber</span> <span class="p">-&gt;</span> <span class="nc">Double</span><span class="p">.</span><span class="nc">NaN</span>
    <span class="c1">// else 절이 필요 없음!</span>
<span class="p">}</span>
</code></pre></div></div>

<h2 id="object">Object</h2>

<h3 id="object-expression-익명-클래스">Object Expression (익명 클래스)</h3>

<p>Java의 anonymous inner class와 유사합니다.</p>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="n">window</span><span class="p">.</span><span class="nf">addMouseListener</span><span class="p">(</span><span class="kd">object</span> <span class="err">: </span><span class="nc">MouseAdapter</span><span class="p">()</span> <span class="p">{</span>
    <span class="k">override</span> <span class="k">fun</span> <span class="nf">mouseClicked</span><span class="p">(</span><span class="n">e</span><span class="p">:</span> <span class="nc">MouseEvent</span><span class="p">)</span> <span class="p">{</span> <span class="o">..</span><span class="p">.</span> <span class="p">}</span>
    <span class="k">override</span> <span class="k">fun</span> <span class="nf">mouseEntered</span><span class="p">(</span><span class="n">e</span><span class="p">:</span> <span class="nc">MouseEvent</span><span class="p">)</span> <span class="p">{</span> <span class="o">..</span><span class="p">.</span> <span class="p">}</span>
<span class="p">})</span>

<span class="c1">// 여러 인터페이스/클래스 상속</span>
<span class="k">open</span> <span class="kd">class</span> <span class="nc">A</span><span class="p">(</span><span class="n">x</span><span class="p">:</span> <span class="nc">Int</span><span class="p">)</span> <span class="p">{</span>
    <span class="k">public</span> <span class="k">open</span> <span class="kd">val</span> <span class="py">y</span><span class="p">:</span> <span class="nc">Int</span> <span class="p">=</span> <span class="n">x</span>
<span class="p">}</span>

<span class="kd">interface</span> <span class="nc">B</span> <span class="p">{</span> <span class="o">..</span><span class="p">.</span> <span class="p">}</span>

<span class="kd">val</span> <span class="py">ab</span><span class="p">:</span> <span class="nc">A</span> <span class="p">=</span> <span class="kd">object</span> <span class="err">: </span><span class="nc">A</span><span class="p">(</span><span class="mi">1</span><span class="p">),</span> <span class="nc">B</span> <span class="p">{</span>
    <span class="k">override</span> <span class="kd">val</span> <span class="py">y</span> <span class="p">=</span> <span class="mi">15</span>
<span class="p">}</span>
</code></pre></div></div>

<h3 id="간단한-object">간단한 Object</h3>

<p>타입 없이 간단한 객체를 생성할 수 있습니다.</p>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">fun</span> <span class="nf">foo</span><span class="p">()</span> <span class="p">{</span>
    <span class="kd">val</span> <span class="py">adHoc</span> <span class="p">=</span> <span class="kd">object</span> <span class="err">{
        var x: </span><span class="nc">Int</span> <span class="p">=</span> <span class="mi">0</span>
        <span class="kd">var</span> <span class="py">y</span><span class="p">:</span> <span class="nc">Int</span> <span class="p">=</span> <span class="mi">0</span>
    <span class="p">}</span>
    <span class="nf">print</span><span class="p">(</span><span class="n">adHoc</span><span class="p">.</span><span class="n">x</span> <span class="p">+</span> <span class="n">adHoc</span><span class="p">.</span><span class="n">y</span><span class="p">)</span>
<span class="p">}</span>
</code></pre></div></div>

<h3 id="object-declaration-singleton">Object Declaration (Singleton)</h3>

<p>Kotlin에서 싱글톤을 선언하는 가장 쉬운 방법입니다.</p>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">object</span> <span class="nc">Resource</span> <span class="p">{</span>
    <span class="kd">val</span> <span class="py">name</span> <span class="p">=</span> <span class="s">"Name"</span>
<span class="p">}</span>

<span class="c1">// 사용</span>
<span class="kd">val</span> <span class="py">resourceName</span> <span class="p">=</span> <span class="nc">Resource</span><span class="p">.</span><span class="n">name</span>
</code></pre></div></div>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">object</span> <span class="nc">DataProviderManager</span> <span class="p">{</span>
    <span class="k">fun</span> <span class="nf">registerDataProvider</span><span class="p">(</span><span class="n">provider</span><span class="p">:</span> <span class="nc">DataProvider</span><span class="p">)</span> <span class="p">{</span> <span class="o">..</span><span class="p">.</span> <span class="p">}</span>

    <span class="kd">val</span> <span class="py">allDataProviders</span><span class="p">:</span> <span class="nc">Collection</span><span class="p">&lt;</span><span class="nc">DataProvider</span><span class="p">&gt;</span>
        <span class="k">get</span><span class="p">()</span> <span class="p">=</span> <span class="o">..</span><span class="p">.</span>
<span class="p">}</span>

<span class="nc">DataProviderManager</span><span class="p">.</span><span class="nf">registerDataProvider</span><span class="p">(</span><span class="o">..</span><span class="p">.)</span>
</code></pre></div></div>

<h3 id="companion-object">Companion Object</h3>

<p>클래스 내부에 static 멤버를 정의하는 방법입니다.</p>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">class</span> <span class="nc">MyClass</span> <span class="p">{</span>
    <span class="k">companion</span> <span class="k">object</span> <span class="nc">Factory</span> <span class="p">{</span>
        <span class="k">fun</span> <span class="nf">create</span><span class="p">():</span> <span class="nc">MyClass</span> <span class="p">=</span> <span class="nc">MyClass</span><span class="p">()</span>
    <span class="p">}</span>
<span class="p">}</span>

<span class="kd">val</span> <span class="py">instance</span> <span class="p">=</span> <span class="nc">MyClass</span><span class="p">.</span><span class="nf">create</span><span class="p">()</span>

<span class="c1">// 이름 생략 가능</span>
<span class="kd">class</span> <span class="nc">MyClass</span> <span class="p">{</span>
    <span class="k">companion</span> <span class="k">object</span> <span class="p">{</span> <span class="p">}</span>
<span class="p">}</span>

<span class="kd">val</span> <span class="py">x</span> <span class="p">=</span> <span class="nc">MyClass</span><span class="p">.</span><span class="nc">Companion</span>
</code></pre></div></div>

<h3 id="companion-object와-인터페이스">Companion Object와 인터페이스</h3>

<p>Companion object도 인터페이스를 구현할 수 있습니다.</p>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">interface</span> <span class="nc">Factory</span><span class="p">&lt;</span><span class="nc">T</span><span class="p">&gt;</span> <span class="p">{</span>
    <span class="k">fun</span> <span class="nf">create</span><span class="p">():</span> <span class="nc">T</span>
<span class="p">}</span>

<span class="kd">class</span> <span class="nc">MyClass</span> <span class="p">{</span>
    <span class="k">companion</span> <span class="k">object</span> <span class="p">:</span> <span class="nc">Factory</span><span class="p">&lt;</span><span class="nc">MyClass</span><span class="p">&gt;</span> <span class="p">{</span>
        <span class="k">override</span> <span class="k">fun</span> <span class="nf">create</span><span class="p">():</span> <span class="nc">MyClass</span> <span class="p">=</span> <span class="nc">MyClass</span><span class="p">()</span>
    <span class="p">}</span>
<span class="p">}</span>
</code></pre></div></div>

<h2 id="표준-라이브러리의-데이터-클래스">표준 라이브러리의 데이터 클래스</h2>

<p>Kotlin 표준 라이브러리에서 제공하는 데이터 클래스들:</p>

<div class="language-kotlin highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nc">Pair</span>  <span class="c1">// 두 값을 담는 클래스</span>
<span class="nc">Triple</span>  <span class="c1">// 세 값을 담는 클래스</span>

<span class="kd">val</span> <span class="py">pair</span> <span class="p">=</span> <span class="nc">Pair</span><span class="p">(</span><span class="s">"key"</span><span class="p">,</span> <span class="s">"value"</span><span class="p">)</span>
<span class="kd">val</span> <span class="p">(</span><span class="py">key</span><span class="p">,</span> <span class="py">value</span><span class="p">)</span> <span class="p">=</span> <span class="n">pair</span>
</code></pre></div></div>

<h2 id="다음-단계">다음 단계</h2>

<p>클래스와 객체에 대해 알아보았습니다. 다음으로 <a href="/kotlin/kotlin-functions-lambda">함수와 람다</a>에 대해 알아보세요.</p>

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