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<title>在Scala中如何避免导入implicit相关的定义 - Homerun</title>
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<meta name="description" content="Scala中的implicit能够让代码变的简洁很多。很多时候我们倾向于把这些implicit相关定义放到一个统一的地方，然后在各个package中应用。但每次用的时候，都需要做类是这样的import： 1
import com.readventure.MyImplicits._ &hellip;">


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<h1 class="entry-title">在Scala中如何避免导入implicit相关的定义</h1>



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<time datetime="2011-03-11T13:06:00+08:00" pubdate data-updated="true">03/11/11</time>

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<div class="entry-content"><p>Scala中的implicit能够让代码变的简洁很多。很多时候我们倾向于把这些implicit相关定义放到一个统一的地方，然后在各个package中应用。但每次用的时候，都需要做类是这样的import：</p>

<figure class='code'><figcaption><span></span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
</pre></td><td class='code'><pre><code class='scala'><span class='line'><span class="k">import</span> <span class="nn">com.readventure.MyImplicits._</span>
</span></code></pre></td></tr></table></div></figure>


<p>下面我告诉大家一个简单的方式，可以避免这种没有必要的imports。</p>

<h2>方法</h2>

<p>我们可以在com/readventure/下面定义下面这个trait：</p>

<figure class='code'><figcaption><span></span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
</pre></td><td class='code'><pre><code class='scala'><span class='line'><span class="k">package</span> <span class="nn">com.readventure</span>
</span><span class='line'>
</span><span class='line'><span class="k">trait</span> <span class="nc">MyImplicits</span> <span class="o">{</span>
</span><span class='line'> <span class="k">implicit</span> <span class="k">def</span> <span class="n">str2opt</span><span class="o">(</span><span class="n">s</span><span class="k">:</span> <span class="kt">String</span><span class="o">)</span> <span class="k">=</span> <span class="nc">Option</span><span class="o">(</span><span class="n">s</span><span class="o">)</span>
</span><span class='line'> <span class="o">...</span>
</span><span class='line'><span class="o">}</span>
</span></code></pre></td></tr></table></div></figure>


<p>然后在每个要用到这些implicit的包下面（比如<code>com.readventure.test1</code>)放置这样叫<code>package.scala</code>的文件（文件名不重要）:</p>

<figure class='code'><figcaption><span></span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
</pre></td><td class='code'><pre><code class='scala'><span class='line'><span class="k">package</span> <span class="nn">com.readventure</span> <span class="c1">// not &#39;package.readventure.test1&#39;</span>
</span><span class='line'><span class="k">package</span> <span class="nn">object</span> <span class="n">test1</span> <span class="k">extends</span> <span class="n">a</span><span class="o">.</span><span class="nc">Implicits</span> <span class="o">{</span> <span class="cm">/* your other stuff goes here */</span><span class="o">}</span>
</span></code></pre></td></tr></table></div></figure>


<p>注意，这里的package的名字，以及package object的名字很重要，必须和相对应的路径对应。这样在<code>MyImplicits</code>里面的所有东西在<code>com.readventure.test1</code>的任何一个类里面都可以用了，不用显式import任何东西。比如：</p>

<figure class='code'><figcaption><span></span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
</pre></td><td class='code'><pre><code class='scala'><span class='line'><span class="k">package</span> <span class="nn">com.readventure.test1</span>
</span><span class='line'>
</span><span class='line'><span class="k">class</span> <span class="nc">SomeClass</span> <span class="o">{</span>
</span><span class='line'> <span class="k">def</span> <span class="n">testImplicit</span><span class="o">(</span><span class="n">str</span><span class="k">:</span> <span class="kt">String</span><span class="o">)</span><span class="k">:</span> <span class="kt">Option</span><span class="o">[</span><span class="kt">String</span><span class="o">]</span> <span class="k">=</span> <span class="n">str</span>
</span><span class='line'><span class="o">}</span>
</span></code></pre></td></tr></table></div></figure>


<p><code>Package object</code>是Scala2.8的新特性，如果有兴趣，可以看看<a href="http://www.artima.com/scalazine/articles/package_objects.html">这里</a>。</p>
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<span class="byline author vcard">Posted by <span class="fn">Dong Wang</span></span>













<time datetime="2011-03-11T13:06:00+08:00" pubdate data-updated="true">03/11/11</time>


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<a class='category' href='/blog/categories/scala/'>Scala</a>, <a class='category' href='/blog/categories/implicit/'>implicit</a>

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