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<h1 id="-">块和绑定</h1>
<p> 每一个Ruby块中，都包含了代码以及对应的绑定。当你定义一个块的时候，它会夺过当时环境的绑定，而当你执行一个带块的方法的时候，它又会传递这个绑定。</p>
<pre><code class="lang-ruby"><span class="hljs-function"><span class="hljs-keyword">def</span> </span>who
person = <span class="hljs-string">"Matz"</span>
<span class="hljs-keyword">yield</span>(<span class="hljs-string">"rocks"</span>)
<span class="hljs-keyword">end</span>
person = <span class="hljs-string">"Matsumoto"</span>
who <span class="hljs-keyword">do</span> |y|
puts(<span class="hljs-string">"<span class="hljs-subst">#{person}</span>, <span class="hljs-subst">#{y}</span> the world"</span>) <span class="hljs-comment"># => Matsumoto, rocks the world</span>
city = <span class="hljs-string">"Tokyo"</span>
<span class="hljs-keyword">end</span>
puts city
<span class="hljs-comment"># => undefined local variable or method 'city' for main:Object (NameError)</span>
</code></pre>
<p> 观察上述代码，块附近的<code>person</code>变量在块被定义之前是一个新的局部变量，而不是<code>who</code>方法中的<code>person</code>变量。因此，块捕获了本地绑定并把它们结合在了一起。你可以在块中定义新的绑定，不过当块的生命周期结束后，它们也就消失了。</p>
<p> DeathKing注：注意变量定义的作用域。在块内部定义的变量不能用于块外部。而预先在块外部定义的变量，经过块的操作后，值会发生改变。</p>
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