236 lines
8.2 KiB
Plaintext
Generated
236 lines
8.2 KiB
Plaintext
Generated
<!DOCTYPE html>
|
|
<html>
|
|
<head>
|
|
<meta charset="utf-8">
|
|
<title>Go by Example: Closures</title>
|
|
<link rel=stylesheet href="site.css">
|
|
</head>
|
|
<script>
|
|
onkeydown = (e) => {
|
|
|
|
if (e.key == "ArrowLeft") {
|
|
window.location.href = 'variadic-functions';
|
|
}
|
|
|
|
|
|
if (e.key == "ArrowRight") {
|
|
window.location.href = 'recursion';
|
|
}
|
|
|
|
}
|
|
</script>
|
|
<body>
|
|
<div class="example" id="closures">
|
|
<h2><a href="./">Go by Example</a>: Closures</h2>
|
|
|
|
<table>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>Go supports <a href="https://en.wikipedia.org/wiki/Anonymous_function"><em>anonymous functions</em></a>,
|
|
which can form <a href="https://en.wikipedia.org/wiki/Closure_(computer_science)"><em>closures</em></a>.
|
|
Anonymous functions are useful when you want to define
|
|
a function inline without having to name it.</p>
|
|
|
|
</td>
|
|
<td class="code empty leading">
|
|
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
<a href="https://go.dev/play/p/NpgpzS8ZG8y"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
|
|
<pre class="chroma"><span class="kn">package</span> <span class="nx">main</span>
|
|
</pre>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<pre class="chroma"><span class="kn">import</span> <span class="s">"fmt"</span>
|
|
</pre>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>This function <code>intSeq</code> returns another function, which
|
|
we define anonymously in the body of <code>intSeq</code>. The
|
|
returned function <em>closes over</em> the variable <code>i</code> to
|
|
form a closure.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<pre class="chroma">
|
|
<span class="kd">func</span> <span class="nf">intSeq</span><span class="p">()</span> <span class="kd">func</span><span class="p">()</span> <span class="kt">int</span> <span class="p">{</span>
|
|
<span class="nx">i</span> <span class="o">:=</span> <span class="mi">0</span>
|
|
<span class="k">return</span> <span class="kd">func</span><span class="p">()</span> <span class="kt">int</span> <span class="p">{</span>
|
|
<span class="nx">i</span><span class="o">++</span>
|
|
<span class="k">return</span> <span class="nx">i</span>
|
|
<span class="p">}</span>
|
|
<span class="p">}</span>
|
|
</pre>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
|
|
</pre>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>We call <code>intSeq</code>, assigning the result (a function)
|
|
to <code>nextInt</code>. This function value captures its
|
|
own <code>i</code> value, which will be updated each time
|
|
we call <code>nextInt</code>.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<pre class="chroma">
|
|
<span class="nx">nextInt</span> <span class="o">:=</span> <span class="nf">intSeq</span><span class="p">()</span>
|
|
</pre>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>See the effect of the closure by calling <code>nextInt</code>
|
|
a few times.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<pre class="chroma">
|
|
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nf">nextInt</span><span class="p">())</span>
|
|
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nf">nextInt</span><span class="p">())</span>
|
|
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nf">nextInt</span><span class="p">())</span>
|
|
</pre>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>To confirm that the state is unique to that
|
|
particular function, create and test a new one.</p>
|
|
|
|
</td>
|
|
<td class="code">
|
|
|
|
<pre class="chroma">
|
|
<span class="nx">newInts</span> <span class="o">:=</span> <span class="nf">intSeq</span><span class="p">()</span>
|
|
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nf">newInts</span><span class="p">())</span>
|
|
<span class="p">}</span>
|
|
</pre>
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
|
|
<table>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<pre class="chroma"><span class="gp">$</span> go run closures.go
|
|
<span class="go">1
|
|
</span><span class="go">2
|
|
</span><span class="go">3
|
|
</span><span class="go">1</span></pre>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>The last feature of functions we’ll look at for now is
|
|
recursion.</p>
|
|
|
|
</td>
|
|
<td class="code empty">
|
|
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
|
|
|
|
<p class="next">
|
|
Next example: <a href="recursion">Recursion</a>.
|
|
</p>
|
|
|
|
|
|
<p class="footer">
|
|
<script>
|
|
window.onload = function() {
|
|
function styleAllTags(tag, style, value){
|
|
document.querySelectorAll(tag).forEach((tag) => {
|
|
tag.style[style] = value
|
|
})
|
|
}
|
|
|
|
var themeButton = document.getElementById('theme-button');
|
|
var body = document.getElementsByTagName('body')[0];
|
|
|
|
function activateTheme(theme) {
|
|
if (theme === 'dark') {
|
|
body.style.color = "#ffffffeb";
|
|
body.style.backgroundColor = "#1a202c";
|
|
styleAllTags('a', 'color', '#ffffffeb')
|
|
styleAllTags('td.code', 'background', '#333333')
|
|
styleAllTags('td.code.empty', 'background', '#1a202c')
|
|
} else {
|
|
body.style.color = "#252519";
|
|
body.style.backgroundColor = "white";
|
|
styleAllTags('a', 'color', '#252519')
|
|
styleAllTags('td.code', 'background', '#f0f0f0')
|
|
styleAllTags('td.code.empty', 'background', 'white')
|
|
}
|
|
localStorage.setItem('theme', theme);
|
|
}
|
|
|
|
var currentTheme = localStorage.getItem('theme');
|
|
if (currentTheme === 'light' || currentTheme === 'dark') {
|
|
activateTheme(currentTheme);
|
|
} else {
|
|
activateTheme('light');
|
|
}
|
|
|
|
themeButton.onclick = function() {
|
|
var newTheme = localStorage.getItem('theme') === 'dark' ? 'light' : 'dark';
|
|
activateTheme(newTheme);
|
|
}
|
|
}
|
|
</script>
|
|
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>
|
|
</p>
|
|
|
|
</div>
|
|
<script>
|
|
var codeLines = [];
|
|
codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import \"fmt\"\u000A');codeLines.push('func intSeq() func() int {\u000A i :\u003D 0\u000A return func() int {\u000A i++\u000A return i\u000A }\u000A}\u000A');codeLines.push('func main() {\u000A');codeLines.push(' nextInt :\u003D intSeq()\u000A');codeLines.push(' fmt.Println(nextInt())\u000A fmt.Println(nextInt())\u000A fmt.Println(nextInt())\u000A');codeLines.push(' newInts :\u003D intSeq()\u000A fmt.Println(newInts())\u000A}\u000A');codeLines.push('');codeLines.push('');
|
|
</script>
|
|
<script src="site.js" async></script>
|
|
</body>
|
|
</html>
|