134 lines
3.0 KiB
Markdown
134 lines
3.0 KiB
Markdown
---
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title: Switch in Go
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localeTitle: 切换到Go
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---
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# 切换到Go
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Go的switch语句是`if`的替代语句。它使用以下语法：
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```go
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fruit := "apple"
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switch fruit {
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case "banana":
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fmt.Printf("Yellow and long.")
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case "apple":
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fmt.Printf("Red and round.")
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case "lemon":
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fmt.Printf("Yellow and round.")
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}
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```
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该程序的输出将是`Red and round.` 。
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首先，我们将变量`fruit`声明为`apple` 。然后我们使用`fruit`变量作为条件表达式。 Go将`fruit`的价值与提供的`cases`进行比较：
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* 水果==“香蕉”（假）
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* 水果==“苹果”（true）
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注意`lemon`没有经过测试。评估返回true后，不再尝试任何案例。
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与`if` ，您可以在switch的条件表达式中声明临时变量：
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```go
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switch fruit := "apple"; fruit {
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case "banana":
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fmt.Printf("Yellow and long.")
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case "apple":
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fmt.Printf("Red and round.")
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case "lemon":
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fmt.Printf("Yellow and round.")
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}
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```
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变量`fruit`不会在switch语句之外访问。
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## 默认和其他情况
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### 默认
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`default`关键字是没有其他情况返回true时的后备情况：
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```go
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switch fruit := "grape"; fruit {
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case "banana":
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fmt.Printf("Yellow and long.")
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case "apple":
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fmt.Printf("Red and round.")
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case "lemon":
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fmt.Printf("Yellow and round.")
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default:
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fmt.Printf("New fruit: %s!", fruit)
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}
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```
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这个节目的输出将是`New fruit: grape!` 。
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### 不同值的相同操作
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以逗号分隔的值列表，用于将条件表达式值与相同的操作进行比较。
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```go
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switch fruit := "lemon"; fruit {
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case "banana", "lemon":
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fmt.Printf("Yellow fruit.")
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default:
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fmt.Printf("This fruit is a color different than yellow.")
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}
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```
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产量： `Yellow fruit.` 。
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### 没有表达
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没有表达式的`switch true`意味着`switch true` 。这是else-if链的替代版本。
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```go
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fruit := "banana"
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switch {
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case fruit == "banana":
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fmt.Printf("Yellow and long.")
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default:
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fmt.Printf("This is not a banana.")
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}
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```
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这会计算`true == (fruit == "banana")` ，simpleiefied to `true == true` ，返回true。
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### 打破
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您可以在switch语句中中断代码以跳过任何更多代码。
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```go
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appleColor := "green"
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switch fruit := "apple"; fruit {
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case "banana":
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fmt.Printf("Yellow and long.")
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case "apple":
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if appleColor == "green" {
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fmt.Printf("This apple is green!")
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break
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}
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fmt.Printf("This apple is tasty!")
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case "lemon":
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fmt.Printf("Yellow and round.")
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}
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```
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输出： `This apple is green!` 。
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### 下通
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跳到下一个案例，其条件是否为真。
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```go
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switch fruit := "banana"; fruit {
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case "banana":
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fmt.Printf("Yellow and long.")
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fallthrough
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case "apple":
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fmt.Printf("Red and round.")
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case "lemon":
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fmt.Printf("Yellow and round.")
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}
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```
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输出： `Yellow and long.`和`Red and round.` 。 |