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Adding a new example: recover

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With thanks to @LaryBattle for the discussion in #46 and
@kilaka for the discussion in #344.

Fixes #46
Closes #344
This commit is contained in:
Eli Bendersky 2021-09-01 08:51:00 -07:00
parent 5525fed5ae
commit 91c8ceec2c
8 changed files with 247 additions and 3 deletions
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1
examples.txt
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@ -41,6 +41,7 @@ Sorting
Sorting by Functions
Panic
Defer
Recover
Collection Functions
String Functions
String Formatting

41
examples/recover/recover.go Normal file
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@ -0,0 +1,41 @@
// Go makes it possible to _recover_ from a panic, by
// using the `recover` built-in function. A `recover` can
// stop a `panic` from aborting the program and let it
// continue with execution instead.
// An example of where this can be useful: a server
// wouldn't want to crash if one of the client connections
// exhibits a critical error. Instead, the server would
// want to close that connection and continue serving
// other clients. In fact, this is what Go's `net/http`
// does by default for HTTP servers.
package main
import "fmt"
// This function panics.
func mayPanic() {
panic("a problem")
}
func main() {
// `recover` must be called within a deferred function.
// When the enclosing function panics, the defer will
// activate and a `recover` call within it will catch
// the panic.
defer func() {
if r := recover(); r != nil {
// The return value of `recover` is the error raised in
// the call to `panic`.
fmt.Println("Recovered. Error:\n", r)
}
}()
mayPanic()
// This code will not run, because `mayPanic` panics.
// The execution of `main` stops at the point of the
// panic and resumes in the deferred closure.
fmt.Println("After mayPanic()")
}

2
examples/recover/recover.hash Normal file
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@ -0,0 +1,2 @@
053ecbddb4f4a1d881aa40086de99da4e78b9990
Sk-SVdofEIZ

2
examples/recover/recover.sh Normal file
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@ -0,0 +1,2 @@
Recovered. Error:
a problem

2
public/collection-functions generated
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@ -9,7 +9,7 @@
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'defer';
window.location.href = 'recover';
}

4
public/defer generated
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@ -14,7 +14,7 @@
if (e.key == "ArrowRight") {
window.location.href = 'collection-functions';
window.location.href = 'recover';
}
}
@ -195,7 +195,7 @@ after being written.</p>
<p class="next">
Next example: <a href="collection-functions">Collection Functions</a>.
Next example: <a href="recover">Recover</a>.
</p>
<p class="footer">

2
public/index.html generated
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@ -113,6 +113,8 @@
<li><a href="defer">Defer</a></li>
<li><a href="recover">Recover</a></li>
<li><a href="collection-functions">Collection Functions</a></li>
<li><a href="string-functions">String Functions</a></li>

196
public/recover generated Normal file
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@ -0,0 +1,196 @@
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example: Recover</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'defer';
}
if (e.key == "ArrowRight") {
window.location.href = 'collection-functions';
}
}
</script>
<body>
<div class="example" id="recover">
<h2><a href="./">Go by Example</a>: Recover</h2>
<table>
<tr>
<td class="docs">
<p>Go makes it possible to <em>recover</em> from a panic, by
using the <code>recover</code> built-in function. A <code>recover</code> can
stop a <code>panic</code> from aborting the program and let it
continue with execution instead.</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
<p>An example of where this can be useful: a server
wouldn&rsquo;t want to crash if one of the client connections
exhibits a critical error. Instead, the server would
want to close that connection and continue serving
other clients. In fact, this is what Go&rsquo;s <code>net/http</code>
does by default for HTTP servers.</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/Sk-SVdofEIZ"><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">&#34;fmt&#34;</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>This function panics.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">func</span> <span class="nf">mayPanic</span><span class="p">()</span> <span class="p">{</span>
<span class="nb">panic</span><span class="p">(</span><span class="s">&#34;a problem&#34;</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p><code>recover</code> must be called within a deferred function.
When the enclosing function panics, the defer will
activate and a <code>recover</code> call within it will catch
the panic.</p>
</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>The return value of <code>recover</code> is the error raised in
the call to <code>panic</code>.</p>
</td>
<td class="code leading">
<pre class="chroma"> <span class="k">defer</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span>
<span class="k">if</span> <span class="nx">r</span> <span class="o">:=</span> <span class="nb">recover</span><span class="p">();</span> <span class="nx">r</span> <span class="o">!=</span> <span class="kc">nil</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</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="s">&#34;Recovered. Error:\n&#34;</span><span class="p">,</span> <span class="nx">r</span><span class="p">)</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="nf">mayPanic</span><span class="p">()</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>This code will not run, because <code>mayPanic</code> panics.
The execution of <code>main</code> stops at the point of the
panic and resumes in the deferred closure.</p>
</td>
<td class="code">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">&#34;After mayPanic()&#34;</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
</td>
<td class="code">
<pre class="chroma"><span class="go">Recovered. Error:
</span><span class="go"> a problem</span></pre>
</td>
</tr>
</table>
<p class="next">
Next example: <a href="collection-functions">Collection Functions</a>.
</p>
<p class="footer">
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/blob/master/examples/recover">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
</p>
</div>
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