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Dan Abramov
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<h1>
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불변성 헬퍼들
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</h1>
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<div class="subHeader"></div>
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<p>React에서는 mutation을 포함해 어떤 데이터 관리 방식도 사용하실 수 있습니다. 하지만 애플리케이션의 성능이 중요한 부분에서 불변의(immutable) 데이터를 사용할 수 있다면, 쉽게 빠른 <code>shouldComponentUpdate()</code> 메소드를 구현해 애플리케이션의 속도를 크게 향상시킬 수 있습니다.</p>
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<p>JavaScript에서 불변성의 데이터를 다루는 것은 <a href="http://clojure.org/">Clojure</a>같이 그것을 위해 디자인된 언어로 다루는 것보다는 어렵습니다. 하지만, React는 간단한 불변성 헬퍼를 제공합니다. <code>update()</code>는 이런 종류의 데이터를 근본적인 변화 <em>없이</em> 쉽게 다루도록 해줍니다. Immutable-js에 관한 좀 더 자세한 정보는 페이스북의 <a href="https://facebook.github.io/immutable-js/docs/">Immutable-js</a>나 <a href="/react/docs/advanced-performance-ko-KR.html">성능 심화</a>을 참조하세요.</p>
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<h2><a class="anchor" name="주요-아이디어"></a>주요 아이디어 <a class="hash-link" href="#주요-아이디어">#</a></h2>
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<p>만약 데이터를 이렇게 변화시킨다면:</p>
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<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="nx">myData</span><span class="p">.</span><span class="nx">x</span><span class="p">.</span><span class="nx">y</span><span class="p">.</span><span class="nx">z</span> <span class="o">=</span> <span class="mi">7</span><span class="p">;</span>
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<span class="c1">// or...</span>
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<span class="nx">myData</span><span class="p">.</span><span class="nx">a</span><span class="p">.</span><span class="nx">b</span><span class="p">.</span><span class="nx">push</span><span class="p">(</span><span class="mi">9</span><span class="p">);</span>
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</code></pre></div>
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<p>이전의 카피가 덮어씌워진다면 어떤 자료가 바뀌었는지 알 방도가 없습니다. 대신에, <code>myData</code>의 새로운 카피를 만들고 오직 변화가 필요한 부분만 바꿀 필요가 있습니다. 그 다음 <code>shouldComponentUpdate()</code> 에서 <code>myData</code>의 이전 카피와 새로운 카피를 <code>===</code> 연산자를 사용하여 비교할 수 있습니다.</p>
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<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kd">var</span> <span class="nx">newData</span> <span class="o">=</span> <span class="nx">deepCopy</span><span class="p">(</span><span class="nx">myData</span><span class="p">);</span>
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<span class="nx">newData</span><span class="p">.</span><span class="nx">x</span><span class="p">.</span><span class="nx">y</span><span class="p">.</span><span class="nx">z</span> <span class="o">=</span> <span class="mi">7</span><span class="p">;</span>
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<span class="nx">newData</span><span class="p">.</span><span class="nx">a</span><span class="p">.</span><span class="nx">b</span><span class="p">.</span><span class="nx">push</span><span class="p">(</span><span class="mi">9</span><span class="p">);</span>
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</code></pre></div>
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<p>하지만 깊은 복사는 비싸고, 가끔은 불가능하기도 합니다. 변화가 필요한 객체만 복제하고, 변화가 없는 객체는 다시 사용하는 방법으로만 비용을 줄일 수 있습니다. 안타깝지만 오늘날의 JavaScript에서는 그 방법이 성가실 수 있습니다:</p>
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<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kd">var</span> <span class="nx">newData</span> <span class="o">=</span> <span class="nx">extend</span><span class="p">(</span><span class="nx">myData</span><span class="p">,</span> <span class="p">{</span>
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<span class="nx">x</span><span class="o">:</span> <span class="nx">extend</span><span class="p">(</span><span class="nx">myData</span><span class="p">.</span><span class="nx">x</span><span class="p">,</span> <span class="p">{</span>
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<span class="nx">y</span><span class="o">:</span> <span class="nx">extend</span><span class="p">(</span><span class="nx">myData</span><span class="p">.</span><span class="nx">x</span><span class="p">.</span><span class="nx">y</span><span class="p">,</span> <span class="p">{</span><span class="nx">z</span><span class="o">:</span> <span class="mi">7</span><span class="p">}),</span>
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<span class="p">}),</span>
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<span class="nx">a</span><span class="o">:</span> <span class="nx">extend</span><span class="p">(</span><span class="nx">myData</span><span class="p">.</span><span class="nx">a</span><span class="p">,</span> <span class="p">{</span><span class="nx">b</span><span class="o">:</span> <span class="nx">myData</span><span class="p">.</span><span class="nx">a</span><span class="p">.</span><span class="nx">b</span><span class="p">.</span><span class="nx">concat</span><span class="p">(</span><span class="mi">9</span><span class="p">)})</span>
|
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<span class="p">});</span>
|
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</code></pre></div>
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<p>이것은 꽤 성능이 좋긴 하지만 (<code>log n</code>개의 객체만 얕은 복사하고, 나머지는 재사용하기 때문에), 일일히 쓰기엔 큰 고통이 따릅니다. 이 반복들을 보세요! 이건 짜증날 뿐만 아니라 버그들을 야기할수도 있습니다.</p>
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<p><code>update()</code>는 이런 패턴 속에서 코드를 더 쉽게 쓸 수 있도록 편의 문법을 제공합니다. 코드는 이렇습니다:</p>
|
|
<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kd">var</span> <span class="nx">update</span> <span class="o">=</span> <span class="nx">require</span><span class="p">(</span><span class="s1">'react-addons-update'</span><span class="p">);</span>
|
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<span class="kd">var</span> <span class="nx">newData</span> <span class="o">=</span> <span class="nx">update</span><span class="p">(</span><span class="nx">myData</span><span class="p">,</span> <span class="p">{</span>
|
|
<span class="nx">x</span><span class="o">:</span> <span class="p">{</span><span class="nx">y</span><span class="o">:</span> <span class="p">{</span><span class="nx">z</span><span class="o">:</span> <span class="p">{</span><span class="nx">$set</span><span class="o">:</span> <span class="mi">7</span><span class="p">}}},</span>
|
|
<span class="nx">a</span><span class="o">:</span> <span class="p">{</span><span class="nx">b</span><span class="o">:</span> <span class="p">{</span><span class="nx">$push</span><span class="o">:</span> <span class="p">[</span><span class="mi">9</span><span class="p">]}}</span>
|
|
<span class="p">});</span>
|
|
</code></pre></div>
|
|
<p>(<a href="http://docs.mongodb.org/manual/core/crud-introduction/#query">MongoDB 쿼리 언어</a>에서 영감을 받은) 이 문법에 익숙해지기에는 시간이 조금 걸리긴 하지만, 쓸모 없는 반복이 없고 정적분석이 가능할 뿐더러 변할 수 있는(mutative) 버전보다 더 많은 타이핑이 필요하지도 않습니다.</p>
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<p><code>$</code>가 앞에 붙어있는 키들은 <em>커맨드</em> 라고 불립니다. "변하는" 자료 구조는 <em>타겟</em> 이라고 불립니다.</p>
|
|
<h2><a class="anchor" name="사용가능한-커맨드들"></a>사용가능한 커맨드들 <a class="hash-link" href="#사용가능한-커맨드들">#</a></h2>
|
|
<ul>
|
|
<li><code>{$push: array}</code> 모든 아이템들을 타겟에 있는 <code>array</code>에 <code>push()</code>합니다.</li>
|
|
<li><code>{$unshift: array}</code> 타겟속 <code>array</code>에 있는 모든 아이템들을 <code>unshift()</code>합니다.</li>
|
|
<li><code>{$splice: array of arrays}</code> <code>arrays</code> 안의 각 아이템들이 <code>splice()</code>를 주어진 인자들을 사용해 호출하게 합니다.</li>
|
|
<li><code>{$set: any}</code> 타겟 전체를 대체합니다.</li>
|
|
<li><code>{$merge: object}</code> 타겟과 <code>object</code>의 키들을 병합합니다.</li>
|
|
<li><code>{$apply: function}</code> 는 지금 값을 함수에 전달하고 새로운 리턴 값으로 업데이트합니다.</li>
|
|
</ul>
|
|
<h2><a class="anchor" name="예제"></a>예제 <a class="hash-link" href="#예제">#</a></h2><h3><a class="anchor" name="간단한-push"></a>간단한 push <a class="hash-link" href="#간단한-push">#</a></h3><div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kd">var</span> <span class="nx">initialArray</span> <span class="o">=</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">];</span>
|
|
<span class="kd">var</span> <span class="nx">newArray</span> <span class="o">=</span> <span class="nx">update</span><span class="p">(</span><span class="nx">initialArray</span><span class="p">,</span> <span class="p">{</span><span class="nx">$push</span><span class="o">:</span> <span class="p">[</span><span class="mi">4</span><span class="p">]});</span> <span class="c1">// => [1, 2, 3, 4]</span>
|
|
</code></pre></div>
|
|
<p><code>initialArray</code> 은 여전히 <code>[1, 2, 3]</code> 입니다.</p>
|
|
<h3><a class="anchor" name="중첩된-컬렉션"></a>중첩된 컬렉션 <a class="hash-link" href="#중첩된-컬렉션">#</a></h3><div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kd">var</span> <span class="nx">collection</span> <span class="o">=</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="p">{</span><span class="nx">a</span><span class="o">:</span> <span class="p">[</span><span class="mi">12</span><span class="p">,</span> <span class="mi">17</span><span class="p">,</span> <span class="mi">15</span><span class="p">]}];</span>
|
|
<span class="kd">var</span> <span class="nx">newCollection</span> <span class="o">=</span> <span class="nx">update</span><span class="p">(</span><span class="nx">collection</span><span class="p">,</span> <span class="p">{</span><span class="mi">2</span><span class="o">:</span> <span class="p">{</span><span class="nx">a</span><span class="o">:</span> <span class="p">{</span><span class="nx">$splice</span><span class="o">:</span> <span class="p">[[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">13</span><span class="p">,</span> <span class="mi">14</span><span class="p">]]}}});</span>
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|
<span class="c1">// => [1, 2, {a: [12, 13, 14, 15]}]</span>
|
|
</code></pre></div>
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|
<p>이것은 <code>collection</code>의 인덱스 <code>2</code>의 키 <code>a</code>에 접근해, 인덱스 <code>1</code>에 있는 한 아이템을 접합(splice)해서(<code>17</code>를 제거하고) <code>13</code>, <code>14</code>를 추가합니다.</p>
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<h3><a class="anchor" name="현재-상태에-의거해-값을-업데이트"></a>현재 상태에 의거해 값을 업데이트 <a class="hash-link" href="#현재-상태에-의거해-값을-업데이트">#</a></h3><div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kd">var</span> <span class="nx">obj</span> <span class="o">=</span> <span class="p">{</span><span class="nx">a</span><span class="o">:</span> <span class="mi">5</span><span class="p">,</span> <span class="nx">b</span><span class="o">:</span> <span class="mi">3</span><span class="p">};</span>
|
|
<span class="kd">var</span> <span class="nx">newObj</span> <span class="o">=</span> <span class="nx">update</span><span class="p">(</span><span class="nx">obj</span><span class="p">,</span> <span class="p">{</span><span class="nx">b</span><span class="o">:</span> <span class="p">{</span><span class="nx">$apply</span><span class="o">:</span> <span class="kd">function</span><span class="p">(</span><span class="nx">x</span><span class="p">)</span> <span class="p">{</span><span class="k">return</span> <span class="nx">x</span> <span class="o">*</span> <span class="mi">2</span><span class="p">;}}});</span>
|
|
<span class="c1">// => {a: 5, b: 6}</span>
|
|
<span class="c1">// 위의 것과 같은 동작을 합니다만, 깊게 중첩된 컬렉션들에서는 더 장황해 집니다.</span>
|
|
<span class="kd">var</span> <span class="nx">newObj2</span> <span class="o">=</span> <span class="nx">update</span><span class="p">(</span><span class="nx">obj</span><span class="p">,</span> <span class="p">{</span><span class="nx">b</span><span class="o">:</span> <span class="p">{</span><span class="nx">$set</span><span class="o">:</span> <span class="nx">obj</span><span class="p">.</span><span class="nx">b</span> <span class="o">*</span> <span class="mi">2</span><span class="p">}});</span>
|
|
</code></pre></div><h3><a class="anchor" name="얕은-합병"></a>(얕은) 합병 <a class="hash-link" href="#얕은-합병">#</a></h3><div class="highlight"><pre><code class="language-js" data-lang="js"><span class="kd">var</span> <span class="nx">obj</span> <span class="o">=</span> <span class="p">{</span><span class="nx">a</span><span class="o">:</span> <span class="mi">5</span><span class="p">,</span> <span class="nx">b</span><span class="o">:</span> <span class="mi">3</span><span class="p">};</span>
|
|
<span class="kd">var</span> <span class="nx">newObj</span> <span class="o">=</span> <span class="nx">update</span><span class="p">(</span><span class="nx">obj</span><span class="p">,</span> <span class="p">{</span><span class="nx">$merge</span><span class="o">:</span> <span class="p">{</span><span class="nx">b</span><span class="o">:</span> <span class="mi">6</span><span class="p">,</span> <span class="nx">c</span><span class="o">:</span> <span class="mi">7</span><span class="p">}});</span> <span class="c1">// => {a: 5, b: 6, c: 7}</span>
|
|
</code></pre></div>
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