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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example: Switch</title>
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</head>
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<div class="example" id="switch">
<h2><a href="./">Go by Example</a>: Switch</h2>
<table>
<tr>
<td class="docs">
<p><em>Switch statements</em> express conditionals across many
branches.</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/TJ4Az0KuLfL"><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>
<span class="kn">import</span> <span class="s">"time"</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>Here’s a basic <code>switch</code>.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="nx">i</span> <span class="o">:=</span> <span class="mi">2</span>
<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>
<span class="k">switch</span> <span class="nx">i</span> <span class="p">{</span>
<span class="k">case</span> <span class="mi">1</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="s">"one"</span><span class="p">)</span>
<span class="k">case</span> <span class="mi">2</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="s">"two"</span><span class="p">)</span>
<span class="k">case</span> <span class="mi">3</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="s">"three"</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>You can use commas to separate multiple expressions
in the same <code>case</code> statement. We use the optional
<code>default</code> case in this example as well.</p>
</td>
<td class="code leading">
<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>
<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>
<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>
<span class="k">default</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="s">"It's a weekday"</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p><code>switch</code> without an expression is an alternate way
to express if/else logic. Here we also show how the
<code>case</code> expressions can be non-constants.</p>
</td>
<td class="code leading">
<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>
<span class="k">switch</span> <span class="p">{</span>
<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>
<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>
<span class="k">default</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="s">"It's after noon"</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>A type <code>switch</code> compares types instead of values. You
can use this to discover the type of an interface
value. In this example, the variable <code>t</code> will have the
type corresponding to its clause.</p>
</td>
<td class="code">
<div class="highlight"><pre> <span class="nx">whatAmI</span> <span class="o">:=</span> <span class="kd">func</span><span class="p">(</span><span class="nx">i</span> <span class="kd">interface</span><span class="p">{})</span> <span class="p">{</span>
<span class="k">switch</span> <span class="nx">t</span> <span class="o">:=</span> <span class="nx">i</span><span class="p">.(</span><span class="kd">type</span><span class="p">)</span> <span class="p">{</span>
<span class="k">case</span> <span class="kt">bool</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="s">"I'm a bool"</span><span class="p">)</span>
<span class="k">case</span> <span class="kt">int</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="s">"I'm an int"</span><span class="p">)</span>
<span class="k">default</span><span class="p">:</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Printf</span><span class="p">(</span><span class="s">"Don't know type %T\n"</span><span class="p">,</span> <span class="nx">t</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="nx">whatAmI</span><span class="p">(</span><span class="kc">true</span><span class="p">)</span>
<span class="nx">whatAmI</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="nx">whatAmI</span><span class="p">(</span><span class="s">"hey"</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
</td>
<td class="code">
<div class="highlight"><pre><span class="gp">$</span> go run switch.go
<span class="go">Write 2 as two</span>
<span class="go">It's a weekday</span>
<span class="go">It's after noon</span>
<span class="go">I'm a bool</span>
<span class="go">I'm an int</span>
<span class="go">Don't know type string</span>
</pre></div>
</td>
</tr>
</table>
<p class="next">
Next example: <a href="arrays">Arrays</a>.
</p>
<p class="footer">
by <a href="https://twitter.com/mmcgrana">@mmcgrana</a> | <a href="mailto:[email protected]">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>
</p>
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