308 lines
16 KiB
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308 lines
16 KiB
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<!DOCTYPE html>
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<html>
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<head>
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<meta charset="utf-8">
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<title>Go в примерах: Ошибки (Errors)</title>
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<script>
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window.location.href = 'goroutines';
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<body>
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<div class="example" id="errors">
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<h2><a href="./">Go в примерах</a>: Ошибки (Errors)</h2>
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<table>
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<tr>
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<td class="docs">
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<p>В Go принято сообщать об ошибках через явное, отдельное
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возвращаемое значение. Это контрастирует с исключениями,
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используемыми в таких языках, как Java и Ruby, и
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перегруженным одиночным значением результата/ошибки,
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иногда используемым в подходе C. Go, позволяет легко
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увидеть, какие функции возвращают ошибки, и обрабатывать
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их, используя те же языковые конструкции, которые
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используются для любых других задач без ошибок.</p>
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</td>
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<td class="code empty leading">
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<a href="http://play.golang.org/p/9-iENtmoI5k" target="_blank"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
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<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="kn">import</span> <span class="p">(</span>
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<span class="s">"errors"</span>
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<span class="s">"fmt"</span>
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<span class="p">)</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>По соглашению, ошибки - это последнее возвращаемое
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значение с типом <code>error</code> в стандартной реализации.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">f1</span><span class="p">(</span><span class="nx">arg</span> <span class="kt">int</span><span class="p">)</span> <span class="p">(</span><span class="kt">int</span><span class="p">,</span> <span class="kt">error</span><span class="p">)</span> <span class="p">{</span>
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<span class="k">if</span> <span class="nx">arg</span> <span class="o">==</span> <span class="mi">42</span> <span class="p">{</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p><code>errors.New</code> создает стандартную <code>ошибку</code> с
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указаннным сообщением</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <span class="k">return</span> <span class="o">-</span><span class="mi">1</span><span class="p">,</span> <span class="nx">errors</span><span class="p">.</span><span class="nx">New</span><span class="p">(</span><span class="s">"can't work with 42"</span><span class="p">)</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <span class="p">}</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Значение <code>nil</code> в поле ошибки, говорит о том, что
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ошибок нет.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <span class="k">return</span> <span class="nx">arg</span> <span class="o">+</span> <span class="mi">3</span><span class="p">,</span> <span class="kc">nil</span>
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<span class="p">}</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Можно использовать пользовательские типы в качестве
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ошибок, применяя к ним метод <code>Error()</code>. Вот вариант
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в примере выше, который использует пользовательский
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тип для явного представления ошибки аргумента.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="kd">type</span> <span class="nx">argError</span> <span class="kd">struct</span> <span class="p">{</span>
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<span class="nx">arg</span> <span class="kt">int</span>
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<span class="nx">prob</span> <span class="kt">string</span>
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<span class="p">}</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="kd">func</span> <span class="p">(</span><span class="nx">e</span> <span class="o">*</span><span class="nx">argError</span><span class="p">)</span> <span class="nx">Error</span><span class="p">()</span> <span class="kt">string</span> <span class="p">{</span>
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<span class="k">return</span> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Sprintf</span><span class="p">(</span><span class="s">"%d - %s"</span><span class="p">,</span> <span class="nx">e</span><span class="p">.</span><span class="nx">arg</span><span class="p">,</span> <span class="nx">e</span><span class="p">.</span><span class="nx">prob</span><span class="p">)</span>
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<span class="p">}</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">f2</span><span class="p">(</span><span class="nx">arg</span> <span class="kt">int</span><span class="p">)</span> <span class="p">(</span><span class="kt">int</span><span class="p">,</span> <span class="kt">error</span><span class="p">)</span> <span class="p">{</span>
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<span class="k">if</span> <span class="nx">arg</span> <span class="o">==</span> <span class="mi">42</span> <span class="p">{</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>В этом случае мы используем синтаксис <code>&argError</code>
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для создания новой структуры, предоставляя
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значения для двух полей <code>arg</code> и <code>prob</code>.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <span class="k">return</span> <span class="o">-</span><span class="mi">1</span><span class="p">,</span> <span class="o">&</span><span class="nx">argError</span><span class="p">{</span><span class="nx">arg</span><span class="p">,</span> <span class="s">"can't work with it"</span><span class="p">}</span>
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<span class="p">}</span>
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<span class="k">return</span> <span class="nx">arg</span> <span class="o">+</span> <span class="mi">3</span><span class="p">,</span> <span class="kc">nil</span>
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<span class="p">}</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Два цикла ниже тестируют каждую из наших функций,
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возвращающих ошибки. Обратите внимание, что
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использование встроенной проверки ошибок в строке
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<code>if</code> является обычный явлением в Go.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <span class="k">for</span> <span class="nx">_</span><span class="p">,</span> <span class="nx">i</span> <span class="o">:=</span> <span class="k">range</span> <span class="p">[]</span><span class="kt">int</span><span class="p">{</span><span class="mi">7</span><span class="p">,</span> <span class="mi">42</span><span class="p">}</span> <span class="p">{</span>
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<span class="k">if</span> <span class="nx">r</span><span class="p">,</span> <span class="nx">e</span> <span class="o">:=</span> <span class="nx">f1</span><span class="p">(</span><span class="nx">i</span><span class="p">);</span> <span class="nx">e</span> <span class="o">!=</span> <span class="kc">nil</span> <span class="p">{</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"f1 failed:"</span><span class="p">,</span> <span class="nx">e</span><span class="p">)</span>
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<span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"f1 worked:"</span><span class="p">,</span> <span class="nx">r</span><span class="p">)</span>
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<span class="p">}</span>
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<span class="p">}</span>
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<span class="k">for</span> <span class="nx">_</span><span class="p">,</span> <span class="nx">i</span> <span class="o">:=</span> <span class="k">range</span> <span class="p">[]</span><span class="kt">int</span><span class="p">{</span><span class="mi">7</span><span class="p">,</span> <span class="mi">42</span><span class="p">}</span> <span class="p">{</span>
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<span class="k">if</span> <span class="nx">r</span><span class="p">,</span> <span class="nx">e</span> <span class="o">:=</span> <span class="nx">f2</span><span class="p">(</span><span class="nx">i</span><span class="p">);</span> <span class="nx">e</span> <span class="o">!=</span> <span class="kc">nil</span> <span class="p">{</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"f2 failed:"</span><span class="p">,</span> <span class="nx">e</span><span class="p">)</span>
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<span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"f2 worked:"</span><span class="p">,</span> <span class="nx">r</span><span class="p">)</span>
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<span class="p">}</span>
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<span class="p">}</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Если вы хотите использовать данные в пользовательской
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ошибке, вам нужно получить ошибку как экземпляр
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пользовательского типа через утверждение типа.</p>
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</td>
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<td class="code">
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<div class="highlight"><pre> <span class="nx">_</span><span class="p">,</span> <span class="nx">e</span> <span class="o">:=</span> <span class="nx">f2</span><span class="p">(</span><span class="mi">42</span><span class="p">)</span>
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<span class="k">if</span> <span class="nx">ae</span><span class="p">,</span> <span class="nx">ok</span> <span class="o">:=</span> <span class="nx">e</span><span class="p">.(</span><span class="o">*</span><span class="nx">argError</span><span class="p">);</span> <span class="nx">ok</span> <span class="p">{</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">ae</span><span class="p">.</span><span class="nx">arg</span><span class="p">)</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">ae</span><span class="p">.</span><span class="nx">prob</span><span class="p">)</span>
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<span class="p">}</span>
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<span class="p">}</span>
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</pre></div>
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</td>
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</tr>
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</table>
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<table>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="gp">$</span> go run errors.go
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<span class="go">f1 worked: 10</span>
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<span class="go">f1 failed: can't work with 42</span>
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<span class="go">f2 worked: 10</span>
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<span class="go">f2 failed: 42 - can't work with it</span>
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<span class="go">42</span>
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<span class="go">can't work with it</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Посмотрите <a href="http://blog.golang.org/2011/07/error-handling-and-go.html">эту статью</a>
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в блоге Go для более подробной информации об ошибках.</p>
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</td>
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<td class="code empty">
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</td>
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</tr>
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</table>
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<p class="next">
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Следующий пример: <a href="goroutines">Горутины (Goroutines)</a>.
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</p>
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<p class="footer">
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by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/errors">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
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<br/>
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переведено Nick S. | <a href="https://github.com/badkaktus/gobyexample">исходники</a>
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</p>
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</div>
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<script>
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var codeLines = [];
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codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import (\u000A \"errors\"\u000A \"fmt\"\u000A)\u000A');codeLines.push('func f1(arg int) (int, error) {\u000A if arg == 42 {\u000A');codeLines.push(' return -1, errors.New(\"can\'t work with 42\")\u000A');codeLines.push(' }\u000A');codeLines.push(' return arg + 3, nil\u000A}\u000A');codeLines.push('type argError struct {\u000A arg int\u000A prob string\u000A}\u000A');codeLines.push('func (e *argError) Error() string {\u000A return fmt.Sprintf(\"%d - %s\", e.arg, e.prob)\u000A}\u000A');codeLines.push('func f2(arg int) (int, error) {\u000A if arg == 42 {\u000A');codeLines.push(' return -1, &argError{arg, \"can\'t work with it\"}\u000A }\u000A return arg + 3, nil\u000A}\u000A');codeLines.push('func main() {\u000A');codeLines.push(' for _, i := range []int{7, 42} {\u000A if r, e := f1(i); e != nil {\u000A fmt.Println(\"f1 failed:\", e)\u000A } else {\u000A fmt.Println(\"f1 worked:\", r)\u000A }\u000A }\u000A for _, i := range []int{7, 42} {\u000A if r, e := f2(i); e != nil {\u000A fmt.Println(\"f2 failed:\", e)\u000A } else {\u000A fmt.Println(\"f2 worked:\", r)\u000A }\u000A }\u000A');codeLines.push(' _, e := f2(42)\u000A if ae, ok := e.(*argError); ok {\u000A fmt.Println(ae.arg)\u000A fmt.Println(ae.prob)\u000A }\u000A}\u000A');codeLines.push('');codeLines.push('');
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</script>
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<script src="site.js" async></script>
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</body>
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</html>
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