239 lines
7.7 KiB
Plaintext
Generated
239 lines
7.7 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: Panic</title>
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<div class="example" id="panic">
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<h2><a href="./">Go by Example</a>: Panic</h2>
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<table>
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<tr>
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<td class="docs">
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<p>A <code>panic</code> typically means something went unexpectedly
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wrong. Mostly we use it to fail fast on errors that
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shouldn’t occur during normal operation, or that we
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aren’t prepared to handle gracefully.</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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<td class="docs">
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</td>
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<td class="code leading">
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<a href="https://go.dev/play/p/9-2vCvRuhmE"><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">"os"</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>We’ll use panic throughout this site to check for
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unexpected errors. This is the only program on the
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site designed to panic.</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="nb">panic</span><span class="p">(</span><span class="s">"a problem"</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 common use of panic is to abort if a function
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returns an error value that we don’t know how to
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(or want to) handle. Here’s an example of
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<code>panic</code>king if we get an unexpected error when creating a new file.</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">_</span><span class="p">,</span> <span class="nx">err</span> <span class="o">:=</span> <span class="nx">os</span><span class="p">.</span><span class="nf">Create</span><span class="p">(</span><span class="s">"/tmp/file"</span><span class="p">)</span>
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<span class="k">if</span> <span class="nx">err</span> <span class="o">!=</span> <span class="kc">nil</span> <span class="p">{</span>
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<span class="nb">panic</span><span class="p">(</span><span class="nx">err</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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<p>Running this program will cause it to panic, print
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an error message and goroutine traces, and exit with
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a non-zero status.</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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<p>When first panic in <code>main</code> fires, the program exits
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without reaching the rest of the code. If you’d like
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to see the program try to create a temp file, comment
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the first panic out.</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="gp">$</span> go run panic.go
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<span class="go">panic: a problem</span></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="go">goroutine 1 [running]:
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</span><span class="go">main.main()
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</span><span class="go"> /.../panic.go:12 +0x47
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</span><span class="go">...
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</span><span class="go">exit status 2</span></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>Note that unlike some languages which use exceptions
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for handling of many errors, in Go it is idiomatic
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to use error-indicating return values wherever possible.</p>
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</td>
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<td class="code empty">
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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="defer">Defer</a>.
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</p>
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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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<script>
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var codeLines = [];
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codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import \"os\"\u000A');codeLines.push('func main() {\u000A');codeLines.push(' panic(\"a problem\")\u000A');codeLines.push(' _, err :\u003D os.Create(\"/tmp/file\")\u000A if err !\u003D nil {\u000A panic(err)\u000A }\u000A}\u000A');codeLines.push('');codeLines.push('');codeLines.push('');codeLines.push('');
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