237 lines
7.9 KiB
Plaintext
Generated
237 lines
7.9 KiB
Plaintext
Generated
<!DOCTYPE html>
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<meta charset="utf-8">
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<title>Go by Example: Constants</title>
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<div class="example" id="constants">
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<h2><a href="./">Go by Example</a>: Constants</h2>
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<table>
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<tr>
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<td class="docs">
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<p>Go supports <em>constants</em> of character, string, boolean,
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and numeric values.</p>
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</td>
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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="https://go.dev/play/p/Vw-pXSfo9_b"><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="p">(</span>
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<span class="s">"fmt"</span>
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<span class="s">"math"</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>const</code> declares a constant value.</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="kd">const</span> <span class="nx">s</span> <span class="kt">string</span> <span class="p">=</span> <span class="s">"constant"</span>
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</pre>
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</td>
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<td class="docs">
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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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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">s</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>A <code>const</code> statement can appear anywhere a <code>var</code>
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statement can.</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="kd">const</span> <span class="nx">n</span> <span class="p">=</span> <span class="mi">500000000</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>Constant expressions perform arithmetic with
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arbitrary precision.</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="kd">const</span> <span class="nx">d</span> <span class="p">=</span> <span class="mf">3e20</span> <span class="o">/</span> <span class="nx">n</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">d</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>A numeric constant has no type until it’s given
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one, such as by an explicit conversion.</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="nb">int64</span><span class="p">(</span><span class="nx">d</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>A number can be given a type by using it in a
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context that requires one, such as a variable
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assignment or function call. For example, here
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<code>math.Sin</code> expects a <code>float64</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="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">math</span><span class="p">.</span><span class="nf">Sin</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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</td>
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<td class="code">
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<pre class="chroma"><span class="gp">$</span> go run constant.go
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<span class="go">constant
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</span><span class="go">6e+11
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</span><span class="go">600000000000
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</span><span class="go">-0.28470407323754404</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="for">For</a>.
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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> | <button id="theme-button">Toggle theme</button>
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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 (\u000A \"fmt\"\u000A \"math\"\u000A)\u000A');codeLines.push('const s string \u003D \"constant\"\u000A');codeLines.push('func main() {\u000A fmt.Println(s)\u000A');codeLines.push(' const n \u003D 500000000\u000A');codeLines.push(' const d \u003D 3e20 / n\u000A fmt.Println(d)\u000A');codeLines.push(' fmt.Println(int64(d))\u000A');codeLines.push(' fmt.Println(math.Sin(n))\u000A}\u000A');codeLines.push('');
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