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.
240 lines
9.3 KiB
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240 lines
9.3 KiB
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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: Maps</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 = 'slices';
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if (e.key == "ArrowRight") {
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window.location.href = 'range';
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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="maps">
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<h2><a href="./">Go by Example</a>: Maps</h2>
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<table>
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<tr>
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<td class="docs">
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<p><em>Maps</em> are Go’s built-in <a href="http://en.wikipedia.org/wiki/Associative_array">associative data type</a>
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(sometimes called <em>hashes</em> or <em>dicts</em> in other languages).</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/agK2Ro2i-Lu"><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">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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<tr>
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<td class="docs">
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<p>To create an empty map, use the builtin <code>make</code>:
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<code>make(map[key-type]val-type)</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="nx">m</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">(</span><span class="kd">map</span><span class="p">[</span><span class="kt">string</span><span class="p">]</span><span class="kt">int</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>Set key/value pairs using typical <code>name[key] = val</code>
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syntax.</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">m</span><span class="p">[</span><span class="s">"k1"</span><span class="p">]</span> <span class="p">=</span> <span class="mi">7</span>
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<span class="nx">m</span><span class="p">[</span><span class="s">"k2"</span><span class="p">]</span> <span class="p">=</span> <span class="mi">13</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>Printing a map with e.g. <code>fmt.Println</code> will show all of
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its key/value pairs.</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">"map:"</span><span class="p">,</span> <span class="nx">m</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>Get a value for a key with <code>name[key]</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="nx">v1</span> <span class="o">:=</span> <span class="nx">m</span><span class="p">[</span><span class="s">"k1"</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">"v1: "</span><span class="p">,</span> <span class="nx">v1</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>The builtin <code>len</code> returns the number of key/value
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pairs when called on a map.</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">"len:"</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="nx">m</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>The builtin <code>delete</code> removes key/value pairs from
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a map.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <span class="nb">delete</span><span class="p">(</span><span class="nx">m</span><span class="p">,</span> <span class="s">"k2"</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">"map:"</span><span class="p">,</span> <span class="nx">m</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>The optional second return value when getting a
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value from a map indicates if the key was present
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in the map. This can be used to disambiguate
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between missing keys and keys with zero values
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like <code>0</code> or <code>""</code>. Here we didn’t need the value
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itself, so we ignored it with the <em>blank identifier</em>
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<code>_</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="nx">_</span><span class="p">,</span> <span class="nx">prs</span> <span class="o">:=</span> <span class="nx">m</span><span class="p">[</span><span class="s">"k2"</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">"prs:"</span><span class="p">,</span> <span class="nx">prs</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 declare and initialize a new map in
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the same line with this syntax.</p>
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</td>
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<td class="code">
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<div class="highlight"><pre> <span class="nx">n</span> <span class="o">:=</span> <span class="kd">map</span><span class="p">[</span><span class="kt">string</span><span class="p">]</span><span class="kt">int</span><span class="p">{</span><span class="s">"foo"</span><span class="p">:</span> <span class="mi">1</span><span class="p">,</span> <span class="s">"bar"</span><span class="p">:</span> <span class="mi">2</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">"map:"</span><span class="p">,</span> <span class="nx">n</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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<p>Note that maps appear in the form <code>map[k:v k:v]</code> when
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printed with <code>fmt.Println</code>.</p>
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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 maps.go
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<span class="go">map: map[k1:7 k2:13]</span>
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<span class="go">v1: 7</span>
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<span class="go">len: 2</span>
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<span class="go">map: map[k1:7]</span>
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<span class="go">prs: false</span>
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<span class="go">map: map[bar:2 foo:1]</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="range">Range</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/maps">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('func main() {\u000A');codeLines.push(' m :\u003D make(map[string]int)\u000A');codeLines.push(' m[\"k1\"] \u003D 7\u000A m[\"k2\"] \u003D 13\u000A');codeLines.push(' fmt.Println(\"map:\", m)\u000A');codeLines.push(' v1 :\u003D m[\"k1\"]\u000A fmt.Println(\"v1: \", v1)\u000A');codeLines.push(' fmt.Println(\"len:\", len(m))\u000A');codeLines.push(' delete(m, \"k2\")\u000A fmt.Println(\"map:\", m)\u000A');codeLines.push(' _, prs :\u003D m[\"k2\"]\u000A fmt.Println(\"prs:\", prs)\u000A');codeLines.push(' n :\u003D map[string]int{\"foo\": 1, \"bar\": 2}\u000A fmt.Println(\"map:\", n)\u000A}\u000A');codeLines.push('');
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