forked from gobyexample-cn/gobyexample-cn.github.io
-
Notifications
You must be signed in to change notification settings - Fork 0
/
switch.html
203 lines (162 loc) · 10.5 KB
/
switch.html
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example 中文版: Switch 分支结构</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'if-else';
}
if (e.key == "ArrowRight") {
window.location.href = 'arrays';
}
}
</script>
<body>
<div class="example" id="switch">
<h2><a href="./">Go by Example 中文版</a>: Switch 分支结构</h2>
<table>
<tr>
<td class="docs">
<p><em>switch</em> 是多分支情况时快捷的条件语句。</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<a href="https://play.studygolang.com/p/MmQyn9nsEJv"><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>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kn">import</span> <span class="p">(</span>
<span class="s">"fmt"</span>
<span class="s">"time"</span>
<span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>一个基本的 <code>switch</code>。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">i</span> <span class="o">:=</span> <span class="mi">2</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Print</span><span class="p">(</span><span class="s">"write "</span><span class="p">,</span> <span class="nx">i</span><span class="p">,</span> <span class="s">" as "</span><span class="p">)</span>
<span class="k">switch</span> <span class="nx">i</span> <span class="p">{</span>
<span class="k">case</span> <span class="mi">1</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">"one"</span><span class="p">)</span>
<span class="k">case</span> <span class="mi">2</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">"two"</span><span class="p">)</span>
<span class="k">case</span> <span class="mi">3</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">"three"</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>在同一个 <code>case</code> 语句中，你可以使用逗号来分隔多个表达式。
在这个例子中，我们还使用了可选的 <code>default</code> 分支。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="k">switch</span> <span class="nx">time</span><span class="p">.</span><span class="nf">Now</span><span class="p">().</span><span class="nf">Weekday</span><span class="p">()</span> <span class="p">{</span>
<span class="k">case</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Saturday</span><span class="p">,</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Sunday</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">"It's the weekend"</span><span class="p">)</span>
<span class="k">default</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">"It's a weekday"</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>不带表达式的 <code>switch</code> 是实现 if/else 逻辑的另一种方式。
这里还展示了 <code>case</code> 表达式也可以不使用常量。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">t</span> <span class="o">:=</span> <span class="nx">time</span><span class="p">.</span><span class="nf">Now</span><span class="p">()</span>
<span class="k">switch</span> <span class="p">{</span>
<span class="k">case</span> <span class="nx">t</span><span class="p">.</span><span class="nf">Hour</span><span class="p">()</span> <span class="p"><</span> <span class="mi">12</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">"It's before noon"</span><span class="p">)</span>
<span class="k">default</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">"It's after noon"</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>类型开关 (<code>type switch</code>) 比较类型而非值。可以用来发现一个接口值的类型。
在这个例子中，变量 <code>t</code> 在每个分支中会有相应的类型。</p>
</td>
<td class="code">
<pre class="chroma">
<span class="nx">whatAmI</span> <span class="o">:=</span> <span class="kd">func</span><span class="p">(</span><span class="nx">i</span> <span class="kd">interface</span><span class="p">{})</span> <span class="p">{</span>
<span class="k">switch</span> <span class="nx">t</span> <span class="o">:=</span> <span class="nx">i</span><span class="p">.(</span><span class="kd">type</span><span class="p">)</span> <span class="p">{</span>
<span class="k">case</span> <span class="kt">bool</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">"I'm a bool"</span><span class="p">)</span>
<span class="k">case</span> <span class="kt">int</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">"I'm an int"</span><span class="p">)</span>
<span class="k">default</span><span class="p">:</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"Don't know type %T\n"</span><span class="p">,</span> <span class="nx">t</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="nf">whatAmI</span><span class="p">(</span><span class="kc">true</span><span class="p">)</span>
<span class="nf">whatAmI</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="nf">whatAmI</span><span class="p">(</span><span class="s">"hey"</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
</td>
<td class="code">
<pre class="chroma"><span class="gp">$</span> go run switch.go
<span class="go">Write 2 as two
</span><span class="go">It's a weekday
</span><span class="go">It's after noon
</span><span class="go">I'm a bool
</span><span class="go">I'm an int
</span><span class="go">Don't know type string</span></pre>
</td>
</tr>
</table>
<p class="next">
下一个例子: <a href="arrays.html">数组</a>
</p>
<p class="footer">
<a href="https://twitter.com/mmcgrana">@mmcgrana</a> 和<a href="https://eli.thegreenplace.net">Eli Bendersky</a>编写 | <a href="https://github.com/gobyexample-cn">gobyexample-cn</a> 翻译 | <a href="https://github.com/gobyexample-cn/gobyexample/issues">反馈</a> | <a href="https://github.com/gobyexample-cn/gobyexample">源码</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a> </p>
</p>
</div>
<script>
var codeLines = [];
codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import (\u000A \"fmt\"\u000A \"time\"\u000A)\u000A');codeLines.push('func main() {\u000A');codeLines.push(' i :\u003D 2\u000A fmt.Print(\"write \", i, \" as \")\u000A switch i {\u000A case 1:\u000A fmt.Println(\"one\")\u000A case 2:\u000A fmt.Println(\"two\")\u000A case 3:\u000A fmt.Println(\"three\")\u000A }\u000A');codeLines.push(' switch time.Now().Weekday() {\u000A case time.Saturday, time.Sunday:\u000A fmt.Println(\"It\'s the weekend\")\u000A default:\u000A fmt.Println(\"It\'s a weekday\")\u000A }\u000A');codeLines.push(' t :\u003D time.Now()\u000A switch {\u000A case t.Hour() \u003C 12:\u000A fmt.Println(\"It\'s before noon\")\u000A default:\u000A fmt.Println(\"It\'s after noon\")\u000A }\u000A');codeLines.push(' whatAmI :\u003D func(i interface{}) {\u000A switch t :\u003D i.(type) {\u000A case bool:\u000A fmt.Println(\"I\'m a bool\")\u000A case int:\u000A fmt.Println(\"I\'m an int\")\u000A default:\u000A fmt.Printf(\"Don\'t know type %T\\n\", t)\u000A }\u000A }\u000A whatAmI(true)\u000A whatAmI(1)\u000A whatAmI(\"hey\")\u000A}\u000A');codeLines.push('');
</script>
<script src="site.js" async></script>
</body>
</html>