223 lines
8.0 KiB
Plaintext
223 lines
8.0 KiB
Plaintext
<!DOCTYPE html>
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<meta http-eqiv="content-type" content="text/html;charset=utf-8">
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<title>Go by Example: Structs</title>
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<div class="example" id="structs">
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<h2><a href="./">Go by Example</a>: Structs</h2>
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<table>
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<tr>
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<td class="docs">
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<p>Go’s <em>structs</em> are typed collections of fields.
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They’re useful for grouping data together to form
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records.</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 class="code leading">
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<a href="http://play.golang.org/p/OMCP5KFC10"><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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</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 <code>person</code> struct type has <code>name</code> and <code>age</code> fields.</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">type</span> <span class="nx">person</span> <span class="kd">struct</span> <span class="p">{</span>
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<span class="nx">name</span> <span class="kt">string</span>
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<span class="nx">age</span> <span class="kt">int</span>
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<span class="p">}</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="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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<td class="docs">
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<p>This syntax creates a new struct.</p>
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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">person</span><span class="p">{</span><span class="s">"Bob"</span><span class="p">,</span> <span class="mi">20</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>You can name the fields when initializing a struct.</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">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>
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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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<p>Omitted fields will be zero-valued.</p>
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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">person</span><span class="p">{</span><span class="nx">name</span><span class="p">:</span> <span class="s">"Fred"</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>An <code>&</code> prefix yields a pointer to the struct.</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="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>
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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>Access struct fields with a dot.</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">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>
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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">s</span><span class="p">.</span><span class="nx">name</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>You can also use dots with struct pointers - the
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pointers are automatically dereferenced.</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">sp</span> <span class="o">:=</span> <span class="o">&</span><span class="nx">s</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">sp</span><span class="p">.</span><span class="nx">age</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>Structs are mutable.</p>
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</td>
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<td class="code">
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<div class="highlight"><pre> <span class="nx">sp</span><span class="p">.</span><span class="nx">age</span> <span class="p">=</span> <span class="mi">51</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">sp</span><span class="p">.</span><span class="nx">age</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">
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<div class="highlight"><pre><span class="gp">$</span> go run structs.go
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<span class="go">{Bob 20}</span>
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<span class="go">{Alice 30}</span>
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<span class="go">{Fred 0}</span>
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<span class="go">&{Ann 40}</span>
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<span class="go">Sean</span>
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<span class="go">50</span>
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<span class="go">51</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="methods">Methods</a>.
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</p>
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<p class="footer">
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<a href="https://twitter.com/gobyexample">@gobyexample</a> | <a href="mailto:mmcgrana@gmail.com">feedback</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/structs">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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