179 lines
6.6 KiB
Plaintext
179 lines
6.6 KiB
Plaintext
<!DOCTYPE html>
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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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<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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<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/zb93qzV6iN3"><img title="Run code" class="run" src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABAAAAAPCAYAAADtc08vAAAABGdBTUEAANbY1E9YMgAAABl0RVh0U29mdHdhcmUAQWRvYmUgSW1hZ2VSZWFkeXHJZTwAAAJ1SURBVCjPY/j//z8DMu7o6GAAgpQgD9tLqcmJH4KDg14aaik/MtdXe2ZjY6OCrh6Fs2jRYmZ9Pd05M9uL/u9dPfU/CLS0dfxvKIz/X5Dg/z8pKdkGqwGpqakMUdExDHJSYqt37tjxf+qUSf9rc2P+79298/+RA3v+H1zV///o6r7/DrbWFQkJiQwxMTGoBjAxMTpKiQmuqMuP/f/xw/v/J0+f/W9tbvTfxVLn/8rJVf+v757z/96hRf8TQtxuCQmLMjk4OKAawMfDVWVvrvd85eTq/7tXTP6/e/XM/22lif9LCnL+b13Q/v/Kzln/L++c/X/7/Jb/VpYWuZFRUagGAAErEBtlxvi+vn944f9L26cDNcz6v21R9/8zm6aC2SBDbu+f/78kK+4/L79AO7oBYCAqxD/57JZp/y/tmPX/wrYZ/6+CbAayD6zs/78daBjIgPayFJAGG6wGAIFAcpjH/dv7F4ANABuya/b/Od3l/ye2V/+/tnv2/7ldxSANmrgMYGBhZg7fuagD7GyYIeeBrrqwdRrQgLn/l02sBGkwwWkAEAjV5EZ/vQV0LswAGAYZsLC3DKTBAJ8BzCkRni/uHFyIYcAtoNc6ypL/ANVIohigrKwMxqqqqgxMzKzM6VHeL+6iGQAKzDtAV5XlJv3n5uFLRTHgzZs3YPzz50+GwqJiPitD9Y8Pjy4BB+CNvfP+3wUmIpAhhckhr3X19LodHZ28UQxQU1MDYw0NDQYBAQEeoBOTK7JjP2xf3Pt/bkfB/4KkoDcKMmIL5OXlFerq6hhu3rzJgC8MwMDYxGSfm5vbVn9/f0cgVxAkpqioyFBfX49iAACbTAK+xT3CzgAAAABJRU5ErkJggg==" /></a>
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<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
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</pre></div>
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<td class="docs">
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<td class="code leading">
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<div class="highlight"><pre><span class="kn">import</span> <span class="s">"fmt"</span>
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</pre></div>
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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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<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>
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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></div>
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</td>
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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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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
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</pre></div>
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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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<div class="highlight"><pre> <span class="nx">nextInt</span> <span class="o">:=</span> <span class="nx">intSeq</span><span class="p">()</span>
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</pre></div>
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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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<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>
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<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>
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<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>
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</pre></div>
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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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<div class="highlight"><pre> <span class="nx">newInts</span> <span class="o">:=</span> <span class="nx">intSeq</span><span class="p">()</span>
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<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>
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<span class="p">}</span>
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</pre></div>
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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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<div class="highlight"><pre><span class="gp">$</span> go run closures.go
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<span class="go">1</span>
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<span class="go">2</span>
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<span class="go">3</span>
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<span class="go">1</span>
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</pre></div>
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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> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/closures">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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</body>
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</html>
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