241 lines
9.6 KiB
Plaintext
Generated
241 lines
9.6 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 Em Exemplos: 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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window.location.href = 'slices';
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window.location.href = 'range';
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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> é o <a href="https://pt.wikipedia.org/wiki/Vetor_associativo">vetor associativo</a>
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nativo de Go.
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(também chamado de <em>hashes</em> ou <em>dicts</em> em outras linguagens).</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 target="_blank" href="https://go.dev/play/p/Z1XbrBn9vsr"><img title="Executar código em nova aba" src="play.png" class="run" /></a><img title="Copiar código" src="clipboard.png" class="copy" />
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<pre class="chroma"><span class="kn">package</span> <span class="nx">main</span>
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</pre>
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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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<pre class="chroma"><span class="kn">import</span> <span class="s">"fmt"</span>
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</pre>
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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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<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
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</pre>
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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>Para criar um map vazio, utilize o comando nativo <code>make</code>:
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<code>make(map[tipoDaChave]tipoDoValor)</code>.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<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>
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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>É possível alterar ou criar pares de chave/valor
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usando a sintaxe <code>nomeDoMap[chave] = valor</code>.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<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>
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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>Ao imprimir um map com <code>fmt.Println</code>, por exemplo,
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serão exibidos todos os pares chave/valor.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"mapa:"</span><span class="p">,</span> <span class="nx">m</span><span class="p">)</span>
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</pre>
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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>Para selecionar o valor de determinada chave,
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usa-se o comando <code>nomeDoMap[chave]</code>.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<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="nf">Println</span><span class="p">(</span><span class="s">"valor 1: "</span><span class="p">,</span> <span class="nx">v1</span><span class="p">)</span>
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</pre>
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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>O comando nativo <code>len</code>, recebendo um mapa como
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argumento, retorna o número de pares chave/valor.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">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>
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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>O comando nativo <code>delete</code> remove um determinado
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par de chave/valor do mapa.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<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="nf">Println</span><span class="p">(</span><span class="s">"mapa:"</span><span class="p">,</span> <span class="nx">m</span><span class="p">)</span>
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</pre>
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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>Ao selecionar um determinado valor em um mapa,
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existe um segundo retorno opcional, do tipo booleano,
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que indica a presença ou ausência de um determinado
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par no map. Isto pode ser utilizado para desambiguação
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entre chaves ausentes e chaves com valor zero, como
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<code>0</code> or <code>""</code>. Onde o valor correspondente à chave não
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for necessário, é possível ignorar com um identificador
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vazio <code>_</code>.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<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="nf">Println</span><span class="p">(</span><span class="s">"presença da chave:"</span><span class="p">,</span> <span class="nx">prs</span><span class="p">)</span>
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</pre>
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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>Também é possível declarar e inicializar um
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novo mapa na mesma linha com a sintaxe a seguir.</p>
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</td>
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<td class="code">
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<pre class="chroma">
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<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="nf">Println</span><span class="p">(</span><span class="s">"mapa:"</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>
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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 que os mapas são exibidos na forma <code>map[k:v k:v]</code>
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quando impressos com <code>fmt.Println</code>.</p>
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</td>
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<td class="code">
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<pre class="chroma">
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<span class="gp">$</span> go run maps.go
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<span class="go">mapa: map[k1:7 k2:13]
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</span><span class="go">valor 1: 7
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</span><span class="go">len: 2
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</span><span class="go">mapa: map[k1:7]
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</span><span class="go">presença da chave: false
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</span><span class="go">mapa: map[bar:2 foo:1]</span></pre>
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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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Próximo exemplo: <a href="range">Range</a>.
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</p>
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<p class="footer">
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Por <a href="https://markmcgranaghan.com">Mark McGranaghan</a> e <a href="https://eli.thegreenplace.net">Eli Bendersky</a> | traduzido por <a href="https://github.com/lucassauro">Lucassauro</a> | <a href="https://github.com/lucassauro/gobyexample">contribua</a> | <a href="https://github.com/mmcgrana/gobyexample#license">licença</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(\"mapa:\", m)\u000A');codeLines.push(' v1 :\u003D m[\"k1\"]\u000A fmt.Println(\"valor 1: \", v1)\u000A');codeLines.push(' fmt.Println(\"len:\", len(m))\u000A');codeLines.push(' delete(m, \"k2\")\u000A fmt.Println(\"mapa:\", m)\u000A');codeLines.push(' _, prs :\u003D m[\"k2\"]\u000A fmt.Println(\"presença da chave:\", prs)\u000A');codeLines.push(' n :\u003D map[string]int{\"foo\": 1, \"bar\": 2}\u000A fmt.Println(\"mapa:\", n)\u000A}\u000A');codeLines.push('');
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</script>
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