205 lines
8.8 KiB
Plaintext
Generated
205 lines
8.8 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 by Example: Range</title>
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<div class="example" id="range">
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<h2><a href="./">Go by Example</a>: Range</h2>
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<table>
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<tr>
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<td class="docs">
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<p><em>range</em> iterates over elements in a variety of data
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structures. Let’s see how to use <code>range</code> with some
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of the data structures we’ve already learned.</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/pdZOtv4g-7J"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" 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>Here we use <code>range</code> to sum the numbers in a slice.
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Arrays work like this too.</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">nums</span> <span class="o">:=</span> <span class="p">[]</span><span class="kt">int</span><span class="p">{</span><span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">}</span>
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<span class="nx">sum</span> <span class="o">:=</span> <span class="mi">0</span>
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<span class="k">for</span> <span class="nx">_</span><span class="p">,</span> <span class="nx">num</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">nums</span> <span class="p">{</span>
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<span class="nx">sum</span> <span class="o">+=</span> <span class="nx">num</span>
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<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">"sum:"</span><span class="p">,</span> <span class="nx">sum</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><code>range</code> on arrays and slices provides both the
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index and value for each entry. Above we didn’t
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need the index, so we ignored it with the
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blank identifier <code>_</code>. Sometimes we actually want
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the indexes though.</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="k">for</span> <span class="nx">i</span><span class="p">,</span> <span class="nx">num</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">nums</span> <span class="p">{</span>
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<span class="k">if</span> <span class="nx">num</span> <span class="o">==</span> <span class="mi">3</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">"index:"</span><span class="p">,</span> <span class="nx">i</span><span class="p">)</span>
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<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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<tr>
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<td class="docs">
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<p><code>range</code> on map iterates over key/value pairs.</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">kvs</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">string</span><span class="p">{</span><span class="s">"a"</span><span class="p">:</span> <span class="s">"apple"</span><span class="p">,</span> <span class="s">"b"</span><span class="p">:</span> <span class="s">"banana"</span><span class="p">}</span>
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<span class="k">for</span> <span class="nx">k</span><span class="p">,</span> <span class="nx">v</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">kvs</span> <span class="p">{</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"%s -> %s\n"</span><span class="p">,</span> <span class="nx">k</span><span class="p">,</span> <span class="nx">v</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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<tr>
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<td class="docs">
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<p><code>range</code> can also iterate over just the keys of a map.</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="k">for</span> <span class="nx">k</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">kvs</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">"key:"</span><span class="p">,</span> <span class="nx">k</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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<tr>
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<td class="docs">
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<p><code>range</code> on strings iterates over Unicode code
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points. The first value is the starting byte index
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of the <code>rune</code> and the second the <code>rune</code> itself.</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="k">for</span> <span class="nx">i</span><span class="p">,</span> <span class="nx">c</span> <span class="o">:=</span> <span class="k">range</span> <span class="s">"go"</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="nx">i</span><span class="p">,</span> <span class="nx">c</span><span class="p">)</span>
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<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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</td>
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<td class="code">
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<pre class="chroma"><span class="gp">$</span> go run range.go
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<span class="go">sum: 9
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</span><span class="go">index: 1
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</span><span class="go">a -> apple
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</span><span class="go">b -> banana
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</span><span class="go">key: a
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</span><span class="go">key: b
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</span><span class="go">0 103
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</span><span class="go">1 111</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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Next example: <a href="functions">Functions</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> and <a href="https://eli.thegreenplace.net">Eli Bendersky</a> | <a href="https://github.com/mmcgrana/gobyexample">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(' nums :\u003D []int{2, 3, 4}\u000A sum :\u003D 0\u000A for _, num :\u003D range nums {\u000A sum +\u003D num\u000A }\u000A fmt.Println(\"sum:\", sum)\u000A');codeLines.push(' for i, num :\u003D range nums {\u000A if num \u003D\u003D 3 {\u000A fmt.Println(\"index:\", i)\u000A }\u000A }\u000A');codeLines.push(' kvs :\u003D map[string]string{\"a\": \"apple\", \"b\": \"banana\"}\u000A for k, v :\u003D range kvs {\u000A fmt.Printf(\"%s -\u003E %s\\n\", k, v)\u000A }\u000A');codeLines.push(' for k :\u003D range kvs {\u000A fmt.Println(\"key:\", k)\u000A }\u000A');codeLines.push(' for i, c :\u003D range \"go\" {\u000A fmt.Println(i, c)\u000A }\u000A}\u000A');codeLines.push('');
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