baf22e84e7
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188 lines
7.9 KiB
Plaintext
188 lines
7.9 KiB
Plaintext
<!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: Methods</title>
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<link rel=stylesheet href="site.css">
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</head>
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<body>
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<div class="example" id="methods">
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<h2><a href="./">Go by Example</a>: Methods</h2>
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<table>
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<tr>
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<td class="docs">
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<p>Go supports <em>methods</em> defined on struct types.</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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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<a href="http://play.golang.org/p/ffMb0txGnYB">
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<img title="Run code" class="run" src="data:image/png;base64,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" />
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</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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</tr>
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<tr>
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<td class="docs">
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</td>
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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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</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">rect</span> <span class="kd">struct</span> <span class="p">{</span>
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<span class="nx">width</span><span class="p">,</span> <span class="nx">height</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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</tr>
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<tr>
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<td class="docs">
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<p>This <code>area</code> method has a <em>receiver type</em> of <code>*rect</code>.</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">func</span> <span class="p">(</span><span class="nx">r</span> <span class="o">*</span><span class="nx">rect</span><span class="p">)</span> <span class="nx">area</span><span class="p">()</span> <span class="kt">int</span> <span class="p">{</span>
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<span class="k">return</span> <span class="nx">r</span><span class="p">.</span><span class="nx">width</span> <span class="o">*</span> <span class="nx">r</span><span class="p">.</span><span class="nx">height</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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<tr>
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<td class="docs">
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<p>Methods can be defined for either pointer or value
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receiver types. Here’s an example of a value receiver.</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">func</span> <span class="p">(</span><span class="nx">r</span> <span class="nx">rect</span><span class="p">)</span> <span class="nx">perim</span><span class="p">()</span> <span class="kt">int</span> <span class="p">{</span>
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<span class="k">return</span> <span class="mi">2</span><span class="o">*</span><span class="nx">r</span><span class="p">.</span><span class="nx">width</span> <span class="o">+</span> <span class="mi">2</span><span class="o">*</span><span class="nx">r</span><span class="p">.</span><span class="nx">height</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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<tr>
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<td class="docs">
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</td>
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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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<span class="nx">r</span> <span class="o">:=</span> <span class="nx">rect</span><span class="p">{</span><span class="nx">width</span><span class="p">:</span> <span class="mi">10</span><span class="p">,</span> <span class="nx">height</span><span class="p">:</span> <span class="mi">5</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>Here we call the 2 methods defined for our 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="s">"area: "</span><span class="p">,</span> <span class="nx">r</span><span class="p">.</span><span class="nx">area</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="s">"perim:"</span><span class="p">,</span> <span class="nx">r</span><span class="p">.</span><span class="nx">perim</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>Go automatically handles conversion between values
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and pointers for method calls. You may want to use
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a pointer receiver type to avoid copying on method
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calls or to allow the method to mutate the
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receiving struct.</p>
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</td>
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<td class="code">
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<div class="highlight"><pre> <span class="nx">rp</span> <span class="o">:=</span> <span class="o">&</span><span class="nx">r</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="s">"area: "</span><span class="p">,</span> <span class="nx">rp</span><span class="p">.</span><span class="nx">area</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="s">"perim:"</span><span class="p">,</span> <span class="nx">rp</span><span class="p">.</span><span class="nx">perim</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 leading">
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<div class="highlight"><pre><span class="gp">$</span> go run methods.go
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<span class="go">area: 50</span>
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<span class="go">perim: 30</span>
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<span class="go">area: 50</span>
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<span class="go">perim: 30</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>Next we’ll look at Go’s mechanism for grouping and
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naming related sets of methods: interfaces.</p>
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</td>
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<td class="code empty">
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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="interfaces">Interfaces</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/methods">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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</body>
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</html>
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