191 lines
6.3 KiB
Plaintext
191 lines
6.3 KiB
Plaintext
<!DOCTYPE html>
|
|
<html>
|
|
<head>
|
|
<meta http-eqiv="content-type" content="text/html;charset=utf-8">
|
|
<title>Go by Example: Closures</title>
|
|
<link rel=stylesheet href="site.css">
|
|
</head>
|
|
<script type="text/javascript">
|
|
if (window.location.host == "gobyexample.com") {
|
|
var _gaq = _gaq || [];
|
|
_gaq.push(['_setAccount', 'UA-34996217-1']);
|
|
_gaq.push(['_trackPageview']);
|
|
(function() {
|
|
var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
|
|
ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
|
|
var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
|
|
})();
|
|
}
|
|
</script>
|
|
<body>
|
|
<div class="example" id="closures">
|
|
<h2><a href="./">Go by Example</a>: Closures</h2>
|
|
|
|
<table>
|
|
|
|
<tr>
|
|
<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>
|
|
|
|
</td>
|
|
<td class="code empty leading">
|
|
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
<a href="http://play.golang.org/p/gQtEWkhWyp"><img title="Run code" src="play.png" class="run" /></a>
|
|
<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<div class="highlight"><pre><span class="kn">import</span> <span class="s">"fmt"</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<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>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
|
|
</td>
|
|
<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>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<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>
|
|
|
|
</td>
|
|
</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>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
|
|
<table>
|
|
|
|
<tr>
|
|
<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>
|
|
|
|
</td>
|
|
</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>
|
|
|
|
<p class="footer">
|
|
by <a href="https://twitter.com/mmcgrana">@mmcgrana</a> | <a href="mailto:mmcgrana@gmail.com">feedback</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/closures">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
|
|
</p>
|
|
</div>
|
|
</body>
|
|
</html>
|