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<title>Go в примерах: Срезы (Slices)</title>
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<div class="example" id="slices">
<h2><a href="./">Go в примерах</a>: Срезы (Slices)</h2>
<table>
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<td class="docs">
<p><em>Срезы</em> являются ключевым типом данных в Go,
предоставляя более мощный интерфейс для последовательностей,
чем массивы.</p>
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<td class="code leading">
<a href="http://play.golang.org/p/32lRsL-MYrP" target="_blank"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
</pre></div>
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<td class="docs">
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<div class="highlight"><pre><span class="kn">import</span> <span class="s">&quot;fmt&quot;</span>
</pre></div>
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<td class="docs">
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<td class="code leading">
<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
</pre></div>
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<td class="docs">
<p>В отличии от массивов, длина среза зависит от содержащихся
в срезе элементов, а не определена при инициализации.
Создать пустой срез в ненулевой длиной можно используя
оператор <code>make</code>. В этом пример мы создаем слайс строк
длиной 3 (заполненный нулевыми значениями).</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">s</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">([]</span><span class="kt">string</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;emp:&quot;</span><span class="p">,</span> <span class="nx">s</span><span class="p">)</span>
</pre></div>
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<td class="docs">
<p>Мы можем устанавливать и получать значения, как в массивах.</p>
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<div class="highlight"><pre> <span class="nx">s</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="p">=</span> <span class="s">&quot;a&quot;</span>
<span class="nx">s</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="p">=</span> <span class="s">&quot;b&quot;</span>
<span class="nx">s</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span> <span class="p">=</span> <span class="s">&quot;c&quot;</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;set:&quot;</span><span class="p">,</span> <span class="nx">s</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;get:&quot;</span><span class="p">,</span> <span class="nx">s</span><span class="p">[</span><span class="mi">2</span><span class="p">])</span>
</pre></div>
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<td class="docs">
<p><code>len</code> возвращает длину среза, как и ожидалось.</p>
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<td class="code leading">
<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;len:&quot;</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="nx">s</span><span class="p">))</span>
</pre></div>
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<td class="docs">
<p>В дополнение к базовой функциональности, срезы
имеют несколько дополнительных особенностей
по сравнению с массивыми. Одна из них - <code>append</code>,
которая возвращает срезу содержащий одно или более
новых значений. Обратите внимание, что результат
функции <code>append</code> необходимо присвоить в переменную,
т.к. это уже будет новый срез.</p>
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<td class="code leading">
<div class="highlight"><pre> <span class="nx">s</span> <span class="p">=</span> <span class="nb">append</span><span class="p">(</span><span class="nx">s</span><span class="p">,</span> <span class="s">&quot;d&quot;</span><span class="p">)</span>
<span class="nx">s</span> <span class="p">=</span> <span class="nb">append</span><span class="p">(</span><span class="nx">s</span><span class="p">,</span> <span class="s">&quot;e&quot;</span><span class="p">,</span> <span class="s">&quot;f&quot;</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;apd:&quot;</span><span class="p">,</span> <span class="nx">s</span><span class="p">)</span>
</pre></div>
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<td class="docs">
<p>Срезы могут быть скопированы с помощью <code>copy</code>. В
данном примере мы создаем пустой срез <code>c</code> такой же
длины как и <code>s</code> и копируем данные из <code>s</code> в <code>c</code>.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">c</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">([]</span><span class="kt">string</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="nx">s</span><span class="p">))</span>
<span class="nb">copy</span><span class="p">(</span><span class="nx">c</span><span class="p">,</span> <span class="nx">s</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;cpy:&quot;</span><span class="p">,</span> <span class="nx">c</span><span class="p">)</span>
</pre></div>
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<td class="docs">
<p>Срезы поддерживают оператор <code>slice</code> (синтаксис
использование <code>slice[low:high]</code>). Для примера,
тут мы получаем срез состоящий из элементов
<code>s[2]</code>, <code>s[3]</code>, и <code>s[4]</code>.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">l</span> <span class="o">:=</span> <span class="nx">s</span><span class="p">[</span><span class="mi">2</span><span class="p">:</span><span class="mi">5</span><span class="p">]</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;sl1:&quot;</span><span class="p">,</span> <span class="nx">l</span><span class="p">)</span>
</pre></div>
</td>
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<td class="docs">
<p>Тут мы получаем срез до элемента <code>s[5]</code> (исключая его).</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">l</span> <span class="p">=</span> <span class="nx">s</span><span class="p">[:</span><span class="mi">5</span><span class="p">]</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;sl2:&quot;</span><span class="p">,</span> <span class="nx">l</span><span class="p">)</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>А тут получаем срез от <code>s[2]</code> (включая его) и до конца
исходного среза.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">l</span> <span class="p">=</span> <span class="nx">s</span><span class="p">[</span><span class="mi">2</span><span class="p">:]</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;sl3:&quot;</span><span class="p">,</span> <span class="nx">l</span><span class="p">)</span>
</pre></div>
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<td class="docs">
<p>Мы можем объявить и заполнить срез значениями в одну
строку.</p>
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<td class="code leading">
<div class="highlight"><pre> <span class="nx">t</span> <span class="o">:=</span> <span class="p">[]</span><span class="kt">string</span><span class="p">{</span><span class="s">&quot;g&quot;</span><span class="p">,</span> <span class="s">&quot;h&quot;</span><span class="p">,</span> <span class="s">&quot;i&quot;</span><span class="p">}</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;dcl:&quot;</span><span class="p">,</span> <span class="nx">t</span><span class="p">)</span>
</pre></div>
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<td class="docs">
<p>Срезы можно объединять в многомерные структуры
данных. Длина внутренних срезов может варьироваться,
в отличии от многомерных массивов.</p>
</td>
<td class="code">
<div class="highlight"><pre> <span class="nx">twoD</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">([][]</span><span class="kt">int</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span>
<span class="k">for</span> <span class="nx">i</span> <span class="o">:=</span> <span class="mi">0</span><span class="p">;</span> <span class="nx">i</span> <span class="p">&lt;</span> <span class="mi">3</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</span> <span class="p">{</span>
<span class="nx">innerLen</span> <span class="o">:=</span> <span class="nx">i</span> <span class="o">+</span> <span class="mi">1</span>
<span class="nx">twoD</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span> <span class="p">=</span> <span class="nb">make</span><span class="p">([]</span><span class="kt">int</span><span class="p">,</span> <span class="nx">innerLen</span><span class="p">)</span>
<span class="k">for</span> <span class="nx">j</span> <span class="o">:=</span> <span class="mi">0</span><span class="p">;</span> <span class="nx">j</span> <span class="p">&lt;</span> <span class="nx">innerLen</span><span class="p">;</span> <span class="nx">j</span><span class="o">++</span> <span class="p">{</span>
<span class="nx">twoD</span><span class="p">[</span><span class="nx">i</span><span class="p">][</span><span class="nx">j</span><span class="p">]</span> <span class="p">=</span> <span class="nx">i</span> <span class="o">+</span> <span class="nx">j</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;2d: &quot;</span><span class="p">,</span> <span class="nx">twoD</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>
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<td class="docs">
<p>Обратите внимание, несмотря на то что срезы
являются отдельным типом данных, отображаются
они так же как массивы командой <code>fmt.Println</code>.</p>
</td>
<td class="code leading">
<div class="highlight"><pre><span class="gp">$</span> go run slices.go
<span class="go">emp: [ ]</span>
<span class="go">set: [a b c]</span>
<span class="go">get: c</span>
<span class="go">len: 3</span>
<span class="go">apd: [a b c d e f]</span>
<span class="go">cpy: [a b c d e f]</span>
<span class="go">sl1: [c d e]</span>
<span class="go">sl2: [a b c d e]</span>
<span class="go">sl3: [c d e f]</span>
<span class="go">dcl: [g h i]</span>
<span class="go">2d: [[0] [1 2] [2 3 4]]</span>
</pre></div>
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<td class="docs">
<p>Посмотрите этот <a href="http://blog.golang.org/2011/01/go-slices-usage-and-internals.html">отличный пост</a>,
написаный командой Go, чтобы узнать больше о разработке
и использовании срезов в Go.</p>
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</td>
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<td class="docs">
<p>Теперь, когда мы рассмотрели массивы и срезы, мы
посмотрим другую ключевую встроенную структуру
данных Go: карты.</p>
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</td>
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</table>
<p class="next">
Следующий пример: <a href="maps">Карты (Maps)</a>.
</p>
<p class="footer">
by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/slices">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
</p>
</div>
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