9e216da9ef
After go1.16, go will use module mode by default, even when the repository is checked out under GOPATH or in a one-off directory. Add go.mod, go.sum to keep this repo buildable without opting out of the module mode. > go mod init github.com/mmcgrana/gobyexample > go mod tidy > go mod vendor In module mode, the 'vendor' directory is special and its contents will be actively maintained by the go command. pygments aren't the dependency the go will know about, so it will delete the contents from vendor directory. Move it to `third_party` directory now. And, vendor the blackfriday package. Note: the tutorial contents are not affected by the change in go1.16 because all the examples in this tutorial ask users to run the go command with the explicit list of files to be compiled (e.g. `go run hello-world.go` or `go build command-line-arguments.go`). When the source list is provided, the go command does not have to compute the build list and whether it's running in GOPATH mode or module mode becomes irrelevant.
180 lines
5.5 KiB
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Generated
180 lines
5.5 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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<link rel=stylesheet href="site.css">
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</head>
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<script>
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onkeydown = (e) => {
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if (e.key == "ArrowLeft") {
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window.location.href = 'sorting-by-functions';
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if (e.key == "ArrowRight") {
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window.location.href = 'defer';
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}
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}
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</script>
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<body>
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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/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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<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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by <a href="https://markmcgranaghan.com">Mark McGranaghan</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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</div>
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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('');
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<script src="site.js" async></script>
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</body>
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</html>
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