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After go1.16, go will use module mode by default, even when the repository is checked out under GOPATH or in a one-off directory. Add go.mod, go.sum to keep this repo buildable without opting out of the module mode. > go mod init github.com/mmcgrana/gobyexample > go mod tidy > go mod vendor In module mode, the 'vendor' directory is special and its contents will be actively maintained by the go command. pygments aren't the dependency the go will know about, so it will delete the contents from vendor directory. Move it to `third_party` directory now. And, vendor the blackfriday package. Note: the tutorial contents are not affected by the change in go1.16 because all the examples in this tutorial ask users to run the go command with the explicit list of files to be compiled (e.g. `go run hello-world.go` or `go build command-line-arguments.go`). When the source list is provided, the go command does not have to compute the build list and whether it's running in GOPATH mode or module mode becomes irrelevant.
205 lines
8.1 KiB
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205 lines
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<!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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<script>
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onkeydown = (e) => {
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if (e.key == "ArrowLeft") {
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window.location.href = 'structs';
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}
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if (e.key == "ArrowRight") {
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window.location.href = 'interfaces';
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}
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}
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</script>
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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/4wmDCAydC1e"><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>
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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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<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 rect struct {\u000A width, height int\u000A}\u000A');codeLines.push('func (r *rect) area() int {\u000A return r.width * r.height\u000A}\u000A');codeLines.push('func (r rect) perim() int {\u000A return 2*r.width + 2*r.height\u000A}\u000A');codeLines.push('func main() {\u000A r :\u003D rect{width: 10, height: 5}\u000A');codeLines.push(' fmt.Println(\"area: \", r.area())\u000A fmt.Println(\"perim:\", r.perim())\u000A');codeLines.push(' rp :\u003D \u0026r\u000A fmt.Println(\"area: \", rp.area())\u000A fmt.Println(\"perim:\", rp.perim())\u000A}\u000A');codeLines.push('');codeLines.push('');
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</script>
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<script src="site.js" async></script>
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</body>
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</html>
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