274 lines
11 KiB
Plaintext
Generated
274 lines
11 KiB
Plaintext
Generated
<!DOCTYPE html>
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<html>
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<head>
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<meta charset="utf-8">
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<title>Go by Example: Structs</title>
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<body>
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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 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/00Yiw6xuICq"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
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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 class="docs">
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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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<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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<p>NewPerson constructs a new person struct with the given name</p>
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<td class="code leading">
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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">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>
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</pre></div>
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</td>
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<td class="docs">
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<p>You can safely return a pointer to local variable
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as a local variable will survive the scope of the function.</p>
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<td class="code leading">
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<div class="highlight"><pre> <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>
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<span class="nx">p</span><span class="p">.</span><span class="nx">age</span> <span class="p">=</span> <span class="mi">42</span>
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<span class="k">return</span> <span class="o">&</span><span class="nx">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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<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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<td class="docs">
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<p>This syntax creates a new 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="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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<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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<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>
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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>It’s idiomatic to encapsulate new struct creation in constructor functions</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">NewPerson</span><span class="p">(</span><span class="s">"Jon"</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>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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<td class="docs">
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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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<span class="go">&{Jon 42}</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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by <a href="https://markmcgranaghan.com">Mark McGranaghan</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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<script>
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var codeLines = [];
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codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import \"fmt\"\u000A');codeLines.push('type person struct {\u000A name string\u000A age int\u000A}\u000A');codeLines.push('func NewPerson(name string) *person {\u000A');codeLines.push(' p := person{name: name}\u000A p.age = 42\u000A return &p\u000A}\u000A');codeLines.push('func main() {\u000A');codeLines.push(' fmt.Println(person{\"Bob\", 20})\u000A');codeLines.push(' fmt.Println(person{name: \"Alice\", age: 30})\u000A');codeLines.push(' fmt.Println(person{name: \"Fred\"})\u000A');codeLines.push(' fmt.Println(&person{name: \"Ann\", age: 40})\u000A');codeLines.push(' fmt.Println(NewPerson(\"Jon\"))\u000A');codeLines.push(' s := person{name: \"Sean\", age: 50}\u000A fmt.Println(s.name)\u000A');codeLines.push(' sp := &s\u000A fmt.Println(sp.age)\u000A');codeLines.push(' sp.age = 51\u000A fmt.Println(sp.age)\u000A}\u000A');codeLines.push('');
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