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interfaces.html
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<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Go por Exemplo: Interfaces</title>
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<div class="example" id="interfaces">
<h2><a href="./">Go por Exemplo</a>: Interfaces</h2>
<table>
<tr>
<td class="docs">
<p><em>Interfaces</em> são coleções nomeadas de
assinaturas de métodos.</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<a href="http://www.go-vim.appspot.com/p/RqIakY1yxL"><img title="Executar código" src="play.png" class="run" /></a>
<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kn">import</span> <span class="s">"fmt"</span>
<span class="kn">import</span> <span class="s">"math"</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>Aqui temos uma interface básica para formas geométricas.</p>
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kd">type</span> <span class="nx">geometria</span> <span class="kd">interface</span> <span class="p">{</span>
<span class="nx">area</span><span class="p">()</span> <span class="kt">float64</span>
<span class="nx">perim</span><span class="p">()</span> <span class="kt">float64</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>Para nosso exemplo vamos implementar essa interface nos
tipos <code>quadrado</code> e <code>círculo</code>.
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kd">type</span> <span class="nx">quadrado</span> <span class="kd">struct</span> <span class="p">{</span>
<span class="nx">largura</span><span class="p">,</span> <span class="nx">altura</span> <span class="kt">float64</span>
<span class="p">}</span>
<span class="kd">type</span> <span class="nx">círculo</span> <span class="kd">struct</span> <span class="p">{</span>
<span class="nx">raio</span> <span class="kt">float64</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>Para implementar uma interface no Go, nós apenas precisamos
implementar todos os métodos na interface. Aqui nós
implementamos <code>geometria</code> nos <code>quadrado</code>s.</p>
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kd">func</span> <span class="p">(</span><span class="nx">q</span> <span class="nx">quadrado</span><span class="p">)</span> <span class="nx">area</span><span class="p">()</span> <span class="kt">float64</span> <span class="p">{</span>
<span class="k">return</span> <span class="nx">q</span><span class="p">.</span><span class="nx">largura</span> <span class="o">*</span> <span class="nx">s</span><span class="p">.</span><span class="nx">altura</span>
<span class="p">}</span>
<span class="kd">func</span> <span class="p">(</span><span class="nx">q</span> <span class="nx">quadrado</span><span class="p">)</span> <span class="nx">perim</span><span class="p">()</span> <span class="kt">float64</span> <span class="p">{</span>
<span class="k">return</span> <span class="mi">2</span><span class="o">*</span><span class="nx">q</span><span class="p">.</span><span class="nx">largura</span> <span class="o">+</span> <span class="mi">2</span><span class="o">*</span><span class="nx">q</span><span class="p">.</span><span class="nx">altura</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>A implementação para <code>círculo</code>s.</p>
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kd">func</span> <span class="p">(</span><span class="nx">c</span> <span class="nx">círculo</span><span class="p">)</span> <span class="nx">area</span><span class="p">()</span> <span class="kt">float64</span> <span class="p">{</span>
<span class="k">return</span> <span class="nx">math</span><span class="p">.</span><span class="nx">Pi</span> <span class="o">*</span> <span class="nx">c</span><span class="p">.</span><span class="nx">raio</span> <span class="o">*</span> <span class="nx">c</span><span class="p">.</span><span class="nx">raio</span>
<span class="p">}</span>
<span class="kd">func</span> <span class="p">(</span><span class="nx">c</span> <span class="nx">círculo</span><span class="p">)</span> <span class="nx">perim</span><span class="p">()</span> <span class="kt">float64</span> <span class="p">{</span>
<span class="k">return</span> <span class="mi">2</span> <span class="o">*</span> <span class="nx">math</span><span class="p">.</span><span class="nx">Pi</span> <span class="o">*</span> <span class="nx">c</span><span class="p">.</span><span class="nx">raio</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>Se a variável possui um tipo inteface, então nós podemos chamar
métodos que estão na interface nomeada. Aqui temos uma
função genérica <code>medida</code> tomando vantagem de seu
trabalho para qualquer <code>geometria</code>.</p>
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kd">func</span> <span class="nx">medir</span><span class="p">(</span><span class="nx">g</span> <span class="nx">geometria</span><span class="p">)</span> <span class="p">{</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">g</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">g</span><span class="p">.</span><span class="nx">area</span><span class="p">())</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">g</span><span class="p">.</span><span class="nx">perim</span><span class="p">())</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
<span class="nx">q</span> <span class="o">:=</span> <span class="nx">quadrado</span><span class="p">{</span><span class="nx">largura</span><span class="p">:</span> <span class="mi">3</span><span class="p">,</span> <span class="nx">altura</span><span class="p">:</span> <span class="mi">4</span><span class="p">}</span>
<span class="nx">c</span> <span class="o">:=</span> <span class="nx">círculo</span><span class="p">{</span><span class="nx">raio</span><span class="p">:</span> <span class="mi">5</span><span class="p">}</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>Os tipos de estruturas <code>círculo</code> e <code>quadrado</code> ambos
implementam a interface <code>geometria</code>, então podemos usar
instâncias dessas estruturas como argumentos para medir.</p>
</td>
<td class="code">
<div class="highlight"><pre> <span class="nx">medir</span><span class="p">(</span><span class="nx">q</span><span class="p">)</span>
<span class="nx">medir</span><span class="p">(</span><span class="nx">c</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
</td>
<td class="code leading">
<div class="highlight"><pre><span class="gp">$</span> go run interfaces.go
<span class="go">{3 4}</span>
<span class="go">12</span>
<span class="go">14</span>
<span class="go">{5}</span>
<span class="go">78.53981633974483</span>
<span class="go">31.41592653589793</span>
</pre></div>
</td>
</tr>
<tr>
<td class="docs">
<p>Para aprender mais sobre interfaces do Go, confira esse
<a href="http://jordanorelli.tumblr.com/post/32665860244/how-to-use-interfaces-in-go">ótima postagem</a>.</p>
</td>
<td class="code empty">
</td>
</tr>
</table>
<p class="next">
Próximo exemplo: <a href="./errors.html">Erros</a>.
</p>
<p class="footer">
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