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| <title>Go by Example: Closures</title> | |
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| <div class="example" id="closures"> | |
| <h2><a href="./">Go by Example</a>: Closures</h2> | |
| <table> | |
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| <td class="docs"> | |
| <p>Go supports <a href="http://en.wikipedia.org/wiki/Anonymous_function"><em>anonymous functions</em></a>, | |
| which can form <a href="http://en.wikipedia.org/wiki/Closure_(computer_science)"><em>closures</em></a>. | |
| Anonymous functions are useful when you want to define | |
| a function inline without having to name it.</p> | |
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| <td class="code empty leading"> | |
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| <td class="docs"> | |
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| <td class="code leading"> | |
| <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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| <td class="code leading"> | |
| <div class="highlight"><pre><span class="kn">import</span> <span class="s">"fmt"</span> | |
| </pre></div> | |
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| <td class="docs"> | |
| <p>This function <code>intSeq</code> returns another function, which | |
| we define anonymously in the body of <code>intSeq</code>. The | |
| returned function <em>closes over</em> the variable <code>i</code> to | |
| form a closure.</p> | |
| </td> | |
| <td class="code leading"> | |
| <div class="highlight"><pre><span class="kd">func</span> <span class="nx">intSeq</span><span class="p">()</span> <span class="kd">func</span><span class="p">()</span> <span class="kt">int</span> <span class="p">{</span> | |
| <span class="nx">i</span> <span class="o">:=</span> <span class="mi">0</span> | |
| <span class="k">return</span> <span class="kd">func</span><span class="p">()</span> <span class="kt">int</span> <span class="p">{</span> | |
| <span class="nx">i</span> <span class="o">+=</span> <span class="mi">1</span> | |
| <span class="k">return</span> <span class="nx">i</span> | |
| <span class="p">}</span> | |
| <span class="p">}</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> | |
| </td> | |
| </tr> | |
| <tr> | |
| <td class="docs"> | |
| <p>We call <code>intSeq</code>, assigning the result (a function) | |
| to <code>nextInt</code>. This function value captures its | |
| own <code>i</code> value, which will be updated each time | |
| we call <code>nextInt</code>.</p> | |
| </td> | |
| <td class="code leading"> | |
| <div class="highlight"><pre> <span class="nx">nextInt</span> <span class="o">:=</span> <span class="nx">intSeq</span><span class="p">()</span> | |
| </pre></div> | |
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| <tr> | |
| <td class="docs"> | |
| <p>See the effect of the closure by calling <code>nextInt</code> | |
| a few times.</p> | |
| </td> | |
| <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="nx">nextInt</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="nx">nextInt</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="nx">nextInt</span><span class="p">())</span> | |
| </pre></div> | |
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| </tr> | |
| <tr> | |
| <td class="docs"> | |
| <p>To confirm that the state is unique to that | |
| particular function, create and test a new one.</p> | |
| </td> | |
| <td class="code"> | |
| <div class="highlight"><pre> <span class="nx">newInts</span> <span class="o">:=</span> <span class="nx">intSeq</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="nx">newInts</span><span class="p">())</span> | |
| <span class="p">}</span> | |
| </pre></div> | |
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| <td class="docs"> | |
| </td> | |
| <td class="code leading"> | |
| <div class="highlight"><pre><span class="gp">$</span> go run closures.go | |
| <span class="go">1</span> | |
| <span class="go">2</span> | |
| <span class="go">3</span> | |
| <span class="go">1</span> | |
| </pre></div> | |
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| </tr> | |
| <tr> | |
| <td class="docs"> | |
| <p>The last feature of functions we’ll look at for now is | |
| recursion.</p> | |
| </td> | |
| <td class="code empty"> | |
| </td> | |
| </tr> | |
| </table> | |
| <p class="next"> | |
| Next example: <a href="recursion">Recursion</a>. | |
| </p> | |
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