173 lines
5.3 KiB
Plaintext
173 lines
5.3 KiB
Plaintext
<!DOCTYPE html>
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<html>
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<head>
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<meta http-eqiv="content-type" content="text/html;charset=utf-8">
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<title>Go by Example: Panic</title>
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<link rel=stylesheet href="site.css">
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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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<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="http://play.golang.org/p/c86oXzfQOt"><img title="Run code" src="play.png" class="run" /></a>
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<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
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</pre></div>
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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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<div class="highlight"><pre><span class="kn">import</span> <span class="s">"os"</span>
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</pre></div>
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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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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
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</pre></div>
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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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<div class="highlight"><pre> <span class="nb">panic</span><span class="p">(</span><span class="s">"a problem"</span><span class="p">)</span>
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</pre></div>
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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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<div class="highlight"><pre> <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="nx">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></div>
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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 leading">
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<div class="highlight"><pre><span class="gp">$</span> go run panic.go
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<span class="go">panic: a problem</span>
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</pre></div>
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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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<div class="highlight"><pre><span class="go">goroutine 1 [running]:</span>
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<span class="go">main.main()</span>
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<span class="go"> /.../panic.go:12 +0x47</span>
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<span class="go">...</span>
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<span class="go">exit status 2</span>
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</pre></div>
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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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<p class="footer">
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<a href="https://twitter.com/gobyexample">@gobyexample</a> | <a href="mailto:mmcgrana@gmail.com">feedback</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/panic">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
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</p>
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