195 lines
6.6 KiB
Plaintext
Generated
195 lines
6.6 KiB
Plaintext
Generated
<!DOCTYPE html>
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<html>
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<head>
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<meta charset="utf-8">
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<title>Go by Example: Closures</title>
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<link rel=stylesheet href="site.css">
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</head>
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<script>
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onkeydown = (e) => {
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if (e.key == "ArrowLeft") {
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window.location.href = 'variadic-functions';
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window.location.href = 'recursion';
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<body>
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<div class="example" id="closures">
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<h2><a href="./">Go by Example</a>: Closures</h2>
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<table>
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<tr>
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<td class="docs">
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<p>Go supports <a href="http://en.wikipedia.org/wiki/Anonymous_function"><em>anonymous functions</em></a>,
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which can form <a href="http://en.wikipedia.org/wiki/Closure_(computer_science)"><em>closures</em></a>.
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Anonymous functions are useful when you want to define
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a function inline without having to name it.</p>
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</td>
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<td class="code empty leading">
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<a href="http://play.golang.org/p/66Lgw9iIIch"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
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<pre class="chroma"><span class="kn">package</span> <span class="nx">main</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<pre class="chroma"><span class="kn">import</span> <span class="s">"fmt"</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>This function <code>intSeq</code> returns another function, which
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we define anonymously in the body of <code>intSeq</code>. The
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returned function <em>closes over</em> the variable <code>i</code> to
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form a closure.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="kd">func</span> <span class="nf">intSeq</span><span class="p">()</span> <span class="kd">func</span><span class="p">()</span> <span class="kt">int</span> <span class="p">{</span>
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<span class="nx">i</span> <span class="o">:=</span> <span class="mi">0</span>
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<span class="k">return</span> <span class="kd">func</span><span class="p">()</span> <span class="kt">int</span> <span class="p">{</span>
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<span class="nx">i</span><span class="o">++</span>
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<span class="k">return</span> <span class="nx">i</span>
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<span class="p">}</span>
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<span class="p">}</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>We call <code>intSeq</code>, assigning the result (a function)
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to <code>nextInt</code>. This function value captures its
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own <code>i</code> value, which will be updated each time
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we call <code>nextInt</code>.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="nx">nextInt</span> <span class="o">:=</span> <span class="nf">intSeq</span><span class="p">()</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>See the effect of the closure by calling <code>nextInt</code>
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a few times.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nf">nextInt</span><span class="p">())</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nf">nextInt</span><span class="p">())</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nf">nextInt</span><span class="p">())</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>To confirm that the state is unique to that
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particular function, create and test a new one.</p>
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</td>
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<td class="code">
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<pre class="chroma">
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<span class="nx">newInts</span> <span class="o">:=</span> <span class="nf">intSeq</span><span class="p">()</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nf">newInts</span><span class="p">())</span>
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<span class="p">}</span>
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</pre>
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</td>
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</tr>
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</table>
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<table>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<pre class="chroma"><span class="gp">$</span> go run closures.go
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<span class="go">1
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</span><span class="go">2
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</span><span class="go">3
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</span><span class="go">1</span></pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>The last feature of functions we’ll look at for now is
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recursion.</p>
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</td>
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<td class="code empty">
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</td>
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</tr>
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</table>
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<p class="next">
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Next example: <a href="recursion">Recursion</a>.
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</p>
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<p class="footer">
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by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> and <a href="https://eli.thegreenplace.net">Eli Bendersky</a> | <a href="https://github.com/mmcgrana/gobyexample">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
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</p>
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</div>
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<script>
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var codeLines = [];
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codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import \"fmt\"\u000A');codeLines.push('func intSeq() func() int {\u000A i :\u003D 0\u000A return func() int {\u000A i++\u000A return i\u000A }\u000A}\u000A');codeLines.push('func main() {\u000A');codeLines.push(' nextInt :\u003D intSeq()\u000A');codeLines.push(' fmt.Println(nextInt())\u000A fmt.Println(nextInt())\u000A fmt.Println(nextInt())\u000A');codeLines.push(' newInts :\u003D intSeq()\u000A fmt.Println(newInts())\u000A}\u000A');codeLines.push('');codeLines.push('');
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