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Clarify zero value for map values when keys don't exist

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This commit is contained in:
Eli Bendersky 2023-03-20 05:59:53 -07:00
parent 38eb2236ca
commit 0812429584
4 changed files with 32 additions and 8 deletions
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6
examples/maps/maps.go
View File

@ -24,6 +24,12 @@ func main() {
v1 := m["k1"]
fmt.Println("v1:", v1)
// If the key doesn't exist, the
// [zero value](https://go.dev/ref/spec#The_zero_value) of the
// value type is returned.
v3 := m["k3"]
fmt.Println("v3:", v3)
// The builtin `len` returns the number of key/value
// pairs when called on a map.
fmt.Println("len:", len(m))

4
examples/maps/maps.hash
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@ -1,2 +1,2 @@
22d147fe9402f9ff210f12b9810811c07f4d64ca
ulCzODwCde_0
0d764945481b4960c573e67f7d303166b750413e
xl_teZEVqbo

1
examples/maps/maps.sh
View File

@ -3,6 +3,7 @@
$ go run maps.go
map: map[k1:7 k2:13]
v1: 7
v3: 0
len: 2
map: map[k1:7]
prs: false

21
public/maps generated
View File

@ -42,7 +42,7 @@
</td>
<td class="code leading">
<a href="https://go.dev/play/p/ulCzODwCde_0"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<a href="https://go.dev/play/p/xl_teZEVqbo"><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>
@ -127,6 +127,22 @@ its key/value pairs.</p>
</td>
</tr>
<tr>
<td class="docs">
<p>If the key doesn&rsquo;t exist, the
<a href="https://go.dev/ref/spec#The_zero_value">zero value</a> of the
value type is returned.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">v3</span> <span class="o">:=</span> <span class="nx">m</span><span class="p">[</span><span class="s">&#34;k3&#34;</span><span class="p">]</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">&#34;v3:&#34;</span><span class="p">,</span> <span class="nx">v3</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>The builtin <code>len</code> returns the number of key/value
@ -208,6 +224,7 @@ printed with <code>fmt.Println</code>.</p>
<span class="gp">$</span> go run maps.go
<span class="go">map: map[k1:7 k2:13]
</span><span class="go">v1: 7
</span><span class="go">v3: 0
</span><span class="go">len: 2
</span><span class="go">map: map[k1:7]
</span><span class="go">prs: false
@ -230,7 +247,7 @@ printed with <code>fmt.Println</code>.</p>
</div>
<script>
var codeLines = [];
codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import \"fmt\"\u000A');codeLines.push('func main() {\u000A');codeLines.push(' m :\u003D make(map[string]int)\u000A');codeLines.push(' m[\"k1\"] \u003D 7\u000A m[\"k2\"] \u003D 13\u000A');codeLines.push(' fmt.Println(\"map:\", m)\u000A');codeLines.push(' v1 :\u003D m[\"k1\"]\u000A fmt.Println(\"v1: \", v1)\u000A');codeLines.push(' fmt.Println(\"len:\", len(m))\u000A');codeLines.push(' delete(m, \"k2\")\u000A fmt.Println(\"map:\", m)\u000A');codeLines.push(' _, prs :\u003D m[\"k2\"]\u000A fmt.Println(\"prs:\", prs)\u000A');codeLines.push(' n :\u003D map[string]int{\"foo\": 1, \"bar\": 2}\u000A fmt.Println(\"map:\", n)\u000A}\u000A');codeLines.push('');
codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import \"fmt\"\u000A');codeLines.push('func main() {\u000A');codeLines.push(' m :\u003D make(map[string]int)\u000A');codeLines.push(' m[\"k1\"] \u003D 7\u000A m[\"k2\"] \u003D 13\u000A');codeLines.push(' fmt.Println(\"map:\", m)\u000A');codeLines.push(' v1 :\u003D m[\"k1\"]\u000A fmt.Println(\"v1:\", v1)\u000A');codeLines.push(' v3 :\u003D m[\"k3\"]\u000A fmt.Println(\"v3:\", v3)\u000A');codeLines.push(' fmt.Println(\"len:\", len(m))\u000A');codeLines.push(' delete(m, \"k2\")\u000A fmt.Println(\"map:\", m)\u000A');codeLines.push(' _, prs :\u003D m[\"k2\"]\u000A fmt.Println(\"prs:\", prs)\u000A');codeLines.push(' n :\u003D map[string]int{\"foo\": 1, \"bar\": 2}\u000A fmt.Println(\"map:\", n)\u000A}\u000A');codeLines.push('');
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