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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example: Structs</title>
<link rel=stylesheet href="site.css">
</head>
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<body>
<div class="example" id="structs">
<h2><a href="./">Go by Example</a>: Structs</h2>
<table>
<tr>
<td class="docs">
<p>Go’s <em>structs</em> are typed collections of fields.
They’re useful for grouping data together to form
records.</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/n7jt1x3iw4Z"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<pre class="chroma"><span class="kn">package</span> <span class="nx">main</span>
</pre>
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<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kn">import</span> <span class="s">"fmt"</span>
</pre>
</td>
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<tr>
<td class="docs">
<p>This <code>person</code> struct type has <code>name</code> and <code>age</code> fields.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">type</span> <span class="nx">person</span> <span class="kd">struct</span> <span class="p">{</span>
<span class="nx">name</span> <span class="kt">string</span>
<span class="nx">age</span> <span class="kt">int</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p><code>newPerson</code> constructs a new person struct with the given name.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">func</span> <span class="nf">newPerson</span><span class="p">(</span><span class="nx">name</span> <span class="kt">string</span><span class="p">)</span> <span class="o">*</span><span class="nx">person</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>You can safely return a pointer to local variable
as a local variable will survive the scope of the function.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">p</span> <span class="o">:=</span> <span class="nx">person</span><span class="p">{</span><span class="nx">name</span><span class="p">:</span> <span class="nx">name</span><span class="p">}</span>
<span class="nx">p</span><span class="p">.</span><span class="nx">age</span> <span class="p">=</span> <span class="mi">42</span>
<span class="k">return</span> <span class="o">&</span><span class="nx">p</span>
<span class="p">}</span>
</pre>
</td>
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<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>This syntax creates a new struct.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">person</span><span class="p">{</span><span class="s">"Bob"</span><span class="p">,</span> <span class="mi">20</span><span class="p">})</span>
</pre>
</td>
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<tr>
<td class="docs">
<p>You can name the fields when initializing a struct.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">person</span><span class="p">{</span><span class="nx">name</span><span class="p">:</span> <span class="s">"Alice"</span><span class="p">,</span> <span class="nx">age</span><span class="p">:</span> <span class="mi">30</span><span class="p">})</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Omitted fields will be zero-valued.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">person</span><span class="p">{</span><span class="nx">name</span><span class="p">:</span> <span class="s">"Fred"</span><span class="p">})</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>An <code>&</code> prefix yields a pointer to the struct.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="o">&</span><span class="nx">person</span><span class="p">{</span><span class="nx">name</span><span class="p">:</span> <span class="s">"Ann"</span><span class="p">,</span> <span class="nx">age</span><span class="p">:</span> <span class="mi">40</span><span class="p">})</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>It’s idiomatic to encapsulate new struct creation in constructor functions</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nf">newPerson</span><span class="p">(</span><span class="s">"Jon"</span><span class="p">))</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Access struct fields with a dot.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">s</span> <span class="o">:=</span> <span class="nx">person</span><span class="p">{</span><span class="nx">name</span><span class="p">:</span> <span class="s">"Sean"</span><span class="p">,</span> <span class="nx">age</span><span class="p">:</span> <span class="mi">50</span><span class="p">}</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">s</span><span class="p">.</span><span class="nx">name</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>You can also use dots with struct pointers - the
pointers are automatically dereferenced.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">sp</span> <span class="o">:=</span> <span class="o">&</span><span class="nx">s</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">sp</span><span class="p">.</span><span class="nx">age</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Structs are mutable.</p>
</td>
<td class="code">
<pre class="chroma">
<span class="nx">sp</span><span class="p">.</span><span class="nx">age</span> <span class="p">=</span> <span class="mi">51</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">sp</span><span class="p">.</span><span class="nx">age</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
</td>
<td class="code">
<pre class="chroma"><span class="gp">$</span> go run structs.go
<span class="go">{Bob 20}
</span><span class="go">{Alice 30}
</span><span class="go">{Fred 0}
</span><span class="go">&{Ann 40}
</span><span class="go">&{Jon 42}
</span><span class="go">Sean
</span><span class="go">50
</span><span class="go">51</span></pre>
</td>
</tr>
</table>
<p class="next">
Next example: <a href="methods">Methods</a>.
</p>
<p class="footer">
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>
</p>
</div>
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