182 lines
5.7 KiB
Plaintext
182 lines
5.7 KiB
Plaintext
<!DOCTYPE html>
|
|
<html>
|
|
<head>
|
|
<meta charset="utf-8">
|
|
<title>Go by Example: Constants</title>
|
|
<link rel=stylesheet href="site.css">
|
|
</head>
|
|
<script type="text/javascript">
|
|
if (window.location.host == "gobyexample.com") {
|
|
var _gaq = _gaq || [];
|
|
_gaq.push(['_setAccount', 'UA-34996217-1']);
|
|
_gaq.push(['_trackPageview']);
|
|
(function() {
|
|
var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
|
|
ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
|
|
var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
|
|
})();
|
|
}
|
|
</script>
|
|
<body>
|
|
<div class="example" id="constants">
|
|
<h2><a href="./">Go by Example</a>: Constants</h2>
|
|
|
|
<table>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>Go supports <em>constants</em> of character, string, boolean,
|
|
and numeric values.</p>
|
|
|
|
</td>
|
|
<td class="code empty leading">
|
|
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
<a href="http://play.golang.org/p/T5sj0eINnp"><img title="Run code" 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><code>const</code> declares a constant value.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<div class="highlight"><pre><span class="kd">const</span> <span class="nx">s</span> <span class="kt">string</span> <span class="p">=</span> <span class="s">"constant"</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">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">s</span><span class="p">)</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>A <code>const</code> statement can appear anywhere a <code>var</code>
|
|
statement can.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<div class="highlight"><pre> <span class="kd">const</span> <span class="nx">n</span> <span class="p">=</span> <span class="mi">500000000</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>Constant expressions perform arithmetic with
|
|
arbitrary precision.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<div class="highlight"><pre> <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>
|
|
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">d</span><span class="p">)</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>A numeric constant has no type until it’s given
|
|
one, such as by an explicit cast.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nb">int64</span><span class="p">(</span><span class="nx">d</span><span class="p">))</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>A number can be given a type by using it in a
|
|
context that requires one, such as a variable
|
|
assignment or function call. For example, here
|
|
<code>math.Sin</code> expects a <code>float64</code>.</p>
|
|
|
|
</td>
|
|
<td class="code">
|
|
|
|
<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">math</span><span class="p">.</span><span class="nx">Sin</span><span class="p">(</span><span class="nx">n</span><span class="p">))</span>
|
|
<span class="p">}</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
|
|
<table>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
|
|
</td>
|
|
<td class="code">
|
|
|
|
<div class="highlight"><pre><span class="gp">$</span> go run constant.go
|
|
<span class="go">constant</span>
|
|
<span class="go">6e+11</span>
|
|
<span class="go">600000000000</span>
|
|
<span class="go">-0.28470407323754404</span>
|
|
</pre></div>
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
|
|
|
|
<p class="next">
|
|
Next example: <a href="for">For</a>.
|
|
</p>
|
|
|
|
<p class="footer">
|
|
by <a href="https://twitter.com/mmcgrana">@mmcgrana</a> | <a href="mailto:mmcgrana@gmail.com">feedback</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/constants">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
|
|
</p>
|
|
</div>
|
|
</body>
|
|
</html>
|