public/structs

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    <div class="example" id="structs">
      <h2><a href="./">Go by Example</a>: Structs</h2>
      
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          <td class="docs">
            <p>Go&rsquo;s <em>structs</em> are typed collections of fields.
They&rsquo;re useful for grouping data together to form
records.</p>

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            <a href="https://go.dev/play/p/ex1J3oieEeo"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
          <pre class="chroma"><code><span class="line"><span class="cl"><span class="kn">package</span> <span class="nx">main</span></span></span></code></pre>
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          <pre class="chroma"><code><span class="line"><span class="cl"><span class="kn">import</span> <span class="s">&#34;fmt&#34;</span></span></span></code></pre>
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            <p>This <code>person</code> struct type has <code>name</code> and <code>age</code> fields.</p>

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          <pre class="chroma"><code><span class="line"><span class="cl"><span class="kd">type</span> <span class="nx">person</span> <span class="kd">struct</span> <span class="p">{</span>
</span></span><span class="line"><span class="cl">    <span class="nx">name</span> <span class="kt">string</span>
</span></span><span class="line"><span class="cl">    <span class="nx">age</span>  <span class="kt">int</span>
</span></span><span class="line"><span class="cl"><span class="p">}</span></span></span></code></pre>
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            <p><code>newPerson</code> constructs a new person struct with the given name.</p>

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          <pre class="chroma"><code><span class="line"><span class="cl"><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></span></span></code></pre>
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          <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>

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          <pre class="chroma"><code><span class="line"><span class="cl">    <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></span><span class="line"><span class="cl">    <span class="nx">p</span><span class="p">.</span><span class="nx">age</span> <span class="p">=</span> <span class="mi">42</span>
</span></span><span class="line"><span class="cl">    <span class="k">return</span> <span class="o">&amp;</span><span class="nx">p</span>
</span></span><span class="line"><span class="cl"><span class="p">}</span></span></span></code></pre>
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          <pre class="chroma"><code><span class="line"><span class="cl"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span></span></span></code></pre>
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            <p>This syntax creates a new struct.</p>

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          <pre class="chroma"><code><span class="line"><span class="cl">    <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">&#34;Bob&#34;</span><span class="p">,</span> <span class="mi">20</span><span class="p">})</span></span></span></code></pre>
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            <p>You can name the fields when initializing a struct.</p>

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          <pre class="chroma"><code><span class="line"><span class="cl">    <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">&#34;Alice&#34;</span><span class="p">,</span> <span class="nx">age</span><span class="p">:</span> <span class="mi">30</span><span class="p">})</span></span></span></code></pre>
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            <p>Omitted fields will be zero-valued.</p>

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          <pre class="chroma"><code><span class="line"><span class="cl">    <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">&#34;Fred&#34;</span><span class="p">})</span></span></span></code></pre>
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            <p>An <code>&amp;</code> prefix yields a pointer to the struct.</p>

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          <pre class="chroma"><code><span class="line"><span class="cl">    <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="o">&amp;</span><span class="nx">person</span><span class="p">{</span><span class="nx">name</span><span class="p">:</span> <span class="s">&#34;Ann&#34;</span><span class="p">,</span> <span class="nx">age</span><span class="p">:</span> <span class="mi">40</span><span class="p">})</span></span></span></code></pre>
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          <td class="docs">
            <p>It&rsquo;s idiomatic to encapsulate new struct creation in constructor functions</p>

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          <pre class="chroma"><code><span class="line"><span class="cl">    <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">&#34;Jon&#34;</span><span class="p">))</span></span></span></code></pre>
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            <p>Access struct fields with a dot.</p>

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          <pre class="chroma"><code><span class="line"><span class="cl">    <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">&#34;Sean&#34;</span><span class="p">,</span> <span class="nx">age</span><span class="p">:</span> <span class="mi">50</span><span class="p">}</span>
</span></span><span class="line"><span class="cl">    <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></span></span></code></pre>
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          <td class="docs">
            <p>You can also use dots with struct pointers - the
pointers are automatically dereferenced.</p>

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          <pre class="chroma"><code><span class="line"><span class="cl">    <span class="nx">sp</span> <span class="o">:=</span> <span class="o">&amp;</span><span class="nx">s</span>
</span></span><span class="line"><span class="cl">    <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></span></code></pre>
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          <td class="docs">
            <p>Structs are mutable.</p>

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          <pre class="chroma"><code><span class="line"><span class="cl">    <span class="nx">sp</span><span class="p">.</span><span class="nx">age</span> <span class="p">=</span> <span class="mi">51</span>
</span></span><span class="line"><span class="cl">    <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></span></code></pre>
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            <p>If a struct type is only used for a single value, we don&rsquo;t
have to give it a name. The value can have an anonymous
struct type. This technique is commonly used for
<a href="testing-and-benchmarking">table-driven tests</a>.</p>

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          <pre class="chroma"><code><span class="line"><span class="cl">    <span class="nx">dog</span> <span class="o">:=</span> <span class="kd">struct</span> <span class="p">{</span>
</span></span><span class="line"><span class="cl">        <span class="nx">name</span>   <span class="kt">string</span>
</span></span><span class="line"><span class="cl">        <span class="nx">isGood</span> <span class="kt">bool</span>
</span></span><span class="line"><span class="cl">    <span class="p">}{</span>
</span></span><span class="line"><span class="cl">        <span class="s">&#34;Rex&#34;</span><span class="p">,</span>
</span></span><span class="line"><span class="cl">        <span class="kc">true</span><span class="p">,</span>
</span></span><span class="line"><span class="cl">    <span class="p">}</span>
</span></span><span class="line"><span class="cl">    <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">dog</span><span class="p">)</span>
</span></span><span class="line"><span class="cl"><span class="p">}</span></span></span></code></pre>
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          <td class="code">
            
          <pre class="chroma"><code><span class="line"><span class="cl"><span class="gp">$</span> go run structs.go
</span></span><span class="line"><span class="cl"><span class="go">{Bob 20}
</span></span></span><span class="line"><span class="cl"><span class="go">{Alice 30}
</span></span></span><span class="line"><span class="cl"><span class="go">{Fred 0}
</span></span></span><span class="line"><span class="cl"><span class="go">&amp;{Ann 40}
</span></span></span><span class="line"><span class="cl"><span class="go">&amp;{Jon 42}
</span></span></span><span class="line"><span class="cl"><span class="go">Sean
</span></span></span><span class="line"><span class="cl"><span class="go">50
</span></span></span><span class="line"><span class="cl"><span class="go">51
</span></span></span><span class="line"><span class="cl"><span class="go">{Rex true}</span></span></span></code></pre>
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        Next example: <a href="methods">Methods</a>.
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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>
    </p>

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