https://ruby-china.org/stephansun en-us <p>《The Ruby Programming Language》5.3.4 Enumerators 这一节中有段代码</p> <pre class="highlight ruby"><code><span class="k">def</span> <span class="nf">twice</span> <span class="k">if</span> <span class="nb">block_given?</span> <span class="k">yield</span> <span class="k">yield</span> <span class="k">else</span> <span class="nb">self</span><span class="p">.</span><span class="nf">to_enum</span><span class="p">(</span><span class="ss">:twice</span><span class="p">)</span> <span class="k">end</span> <span class="k">end</span> </code></pre> <p>没看懂，原文中说 You can duplicate this behavior in your own iterator methods by returning <code>self.to_enum</code> when no block is supplied. Here, for example, is a version of the the <code>twice</code> iterator shown earlier that can return an enumerator if no block is provided:</p> <p>但是这样写有什么实际意义吗？</p> stephansun Mon, 17 Mar 2014 13:58:20 +0800 https://ruby-china.org/topics/17938 https://ruby-china.org/topics/17938