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Hana 9e216da9ef go.mod: add go.mod and move pygments to third_party 
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.
2021-02-15 16:45:26 -05:00

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<!DOCTYPE html>
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<title>Go by Example: Range</title>
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<div class="example" id="range">
<h2><a href="./">Go by Example</a>: Range</h2>
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<p><em>range</em> iterates over elements in a variety of data
structures. Let&rsquo;s see how to use <code>range</code> with some
of the data structures we&rsquo;ve already learned.</p>
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<a href="http://play.golang.org/p/pdZOtv4g-7J"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
</pre></div>
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<div class="highlight"><pre><span class="kn">import</span> <span class="s">&quot;fmt&quot;</span>
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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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<td class="docs">
<p>Here we use <code>range</code> to sum the numbers in a slice.
Arrays work like this too.</p>
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<div class="highlight"><pre> <span class="nx">nums</span> <span class="o">:=</span> <span class="p">[]</span><span class="kt">int</span><span class="p">{</span><span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">}</span>
<span class="nx">sum</span> <span class="o">:=</span> <span class="mi">0</span>
<span class="k">for</span> <span class="nx">_</span><span class="p">,</span> <span class="nx">num</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">nums</span> <span class="p">{</span>
<span class="nx">sum</span> <span class="o">+=</span> <span class="nx">num</span>
<span class="p">}</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;sum:&quot;</span><span class="p">,</span> <span class="nx">sum</span><span class="p">)</span>
</pre></div>
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<p><code>range</code> on arrays and slices provides both the
index and value for each entry. Above we didn&rsquo;t
need the index, so we ignored it with the
blank identifier <code>_</code>. Sometimes we actually want
the indexes though.</p>
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<div class="highlight"><pre> <span class="k">for</span> <span class="nx">i</span><span class="p">,</span> <span class="nx">num</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">nums</span> <span class="p">{</span>
<span class="k">if</span> <span class="nx">num</span> <span class="o">==</span> <span class="mi">3</span> <span class="p">{</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;index:&quot;</span><span class="p">,</span> <span class="nx">i</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}</span>
</pre></div>
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<p><code>range</code> on map iterates over key/value pairs.</p>
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<div class="highlight"><pre> <span class="nx">kvs</span> <span class="o">:=</span> <span class="kd">map</span><span class="p">[</span><span class="kt">string</span><span class="p">]</span><span class="kt">string</span><span class="p">{</span><span class="s">&quot;a&quot;</span><span class="p">:</span> <span class="s">&quot;apple&quot;</span><span class="p">,</span> <span class="s">&quot;b&quot;</span><span class="p">:</span> <span class="s">&quot;banana&quot;</span><span class="p">}</span>
<span class="k">for</span> <span class="nx">k</span><span class="p">,</span> <span class="nx">v</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">kvs</span> <span class="p">{</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Printf</span><span class="p">(</span><span class="s">&quot;%s -&gt; %s\n&quot;</span><span class="p">,</span> <span class="nx">k</span><span class="p">,</span> <span class="nx">v</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>
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<td class="docs">
<p><code>range</code> can also iterate over just the keys of a map.</p>
</td>
<td class="code leading">
<div class="highlight"><pre> <span class="k">for</span> <span class="nx">k</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">kvs</span> <span class="p">{</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;key:&quot;</span><span class="p">,</span> <span class="nx">k</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>
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<td class="docs">
<p><code>range</code> on strings iterates over Unicode code
points. The first value is the starting byte index
of the <code>rune</code> and the second the <code>rune</code> itself.</p>
</td>
<td class="code">
<div class="highlight"><pre> <span class="k">for</span> <span class="nx">i</span><span class="p">,</span> <span class="nx">c</span> <span class="o">:=</span> <span class="k">range</span> <span class="s">&quot;go&quot;</span> <span class="p">{</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">i</span><span class="p">,</span> <span class="nx">c</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}</span>
</pre></div>
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<td class="docs">
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<div class="highlight"><pre><span class="gp">$</span> go run range.go
<span class="go">sum: 9</span>
<span class="go">index: 1</span>
<span class="go">a -&gt; apple</span>
<span class="go">b -&gt; banana</span>
<span class="go">key: a</span>
<span class="go">key: b</span>
<span class="go">0 103</span>
<span class="go">1 111</span>
</pre></div>
</td>
</tr>
</table>
<p class="next">
Next example: <a href="functions">Functions</a>.
</p>
<p class="footer">
by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/range">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
</p>
</div>
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