171 lines
7.0 KiB
Plaintext
171 lines
7.0 KiB
Plaintext
<!DOCTYPE html>
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<html>
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<head>
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<meta http-eqiv="content-type" content="text/html;charset=utf-8">
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<title>Go by Example: Switch</title>
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<div class="example" id="switch">
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<h2><a href="./">Go by Example</a>: Switch</h2>
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<table>
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<tr>
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<td class="docs">
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<p><em>Switch statements</em> express conditionals across many
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branches.</p>
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</td>
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<td class="code empty leading">
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</td>
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<td class="docs">
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<td class="code leading">
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<a href="http://play.golang.org/p/8b5CajPcHn"><img title="Run code" src="play.png" class="run" /></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>
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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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<span class="kn">import</span> <span class="s">"time"</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 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>Here’s a basic <code>switch</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">i</span> <span class="o">:=</span> <span class="mi">2</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Print</span><span class="p">(</span><span class="s">"write "</span><span class="p">,</span> <span class="nx">i</span><span class="p">,</span> <span class="s">" as "</span><span class="p">)</span>
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<span class="k">switch</span> <span class="nx">i</span> <span class="p">{</span>
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<span class="k">case</span> <span class="mi">1</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="s">"one"</span><span class="p">)</span>
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<span class="k">case</span> <span class="mi">2</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="s">"two"</span><span class="p">)</span>
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<span class="k">case</span> <span class="mi">3</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="s">"three"</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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<tr>
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<td class="docs">
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<p>You can use commas to separate multiple expressions
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in the same <code>case</code> statement. We use the optional
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<code>default</code> case in this example as well.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <span class="k">switch</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Now</span><span class="p">().</span><span class="nx">Weekday</span><span class="p">()</span> <span class="p">{</span>
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<span class="k">case</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Saturday</span><span class="p">,</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Sunday</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="s">"it's the weekend"</span><span class="p">)</span>
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<span class="k">default</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="s">"it's a weekday"</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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<tr>
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<td class="docs">
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<p><code>switch</code> without an expression is an alternate way
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to express if/else logic. Here we also show how the
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<code>case</code> expressions can be non-constants.</p>
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</td>
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<td class="code">
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<div class="highlight"><pre> <span class="nx">t</span> <span class="o">:=</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Now</span><span class="p">()</span>
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<span class="k">switch</span> <span class="p">{</span>
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<span class="k">case</span> <span class="nx">t</span><span class="p">.</span><span class="nx">Hour</span><span class="p">()</span> <span class="p"><</span> <span class="mi">12</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="s">"it's before noon"</span><span class="p">)</span>
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<span class="k">default</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="s">"it's after noon"</span><span class="p">)</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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</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">
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<div class="highlight"><pre><span class="gp">$</span> go run switch.go
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<span class="go">write 2 as two</span>
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<span class="go">it's the weekend</span>
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<span class="go">it's before noon</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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<p class="next">
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Next example: <a href="arrays">Arrays</a>.
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</p>
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<p class="footer">
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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/switch">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
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</p>
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