9e216da9ef
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.
274 lines
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274 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: Structs</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 = 'pointers';
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}
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if (e.key == "ArrowRight") {
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window.location.href = 'methods';
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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="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/n7jt1x3iw4Z"><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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<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 class="docs">
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<p><code>newPerson</code> constructs a new person struct with the given name.</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="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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</tr>
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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>
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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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<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">&{Jon 42}</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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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 :\u003D person{name: name}\u000A p.age \u003D 42\u000A return \u0026p\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(\u0026person{name: \"Ann\", age: 40})\u000A');codeLines.push(' fmt.Println(newPerson(\"Jon\"))\u000A');codeLines.push(' s :\u003D person{name: \"Sean\", age: 50}\u000A fmt.Println(s.name)\u000A');codeLines.push(' sp :\u003D \u0026s\u000A fmt.Println(sp.age)\u000A');codeLines.push(' sp.age \u003D 51\u000A fmt.Println(sp.age)\u000A}\u000A');codeLines.push('');
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