英文:
golang switch got an ` used as value` error?
问题
我不太清楚为什么 switch t := some.(type){} 能正常工作，但如果我尝试 switch k := f.Kind(){} 或类似的代码，会出现以下错误：
.\mym.go:58: k := f.Kind() 作为值使用
退出状态 2
英文:
I don't know really why switch t := some.(type){} works well, but if I tried switch k := f.Kind(){} or so on.
.\mym.go:58: k := f.Kind() used as value
exit status 2
答案1
得分: 4
是的，你是对的，这是语法错误；应该是SimpleStmt或ExprSwitchStmt = "switch" [ SimpleStmt ";" ] [ Expression ] "{" { ExprCaseClause } "}"。
参考：
https://golang.org/ref/spec#Switch_statements
在表达式switch中，case包含与switch表达式的值进行比较的表达式。
以下代码将正常工作：
package main
import (
"fmt"
)
type Test struct {
kind int
}
func (s *Test) Kind() int {
return s.kind
}
func main() {
f := &Test{12}
//fmt.Println(k := f.Kind()) //语法错误：意外的:=，期望逗号或)
switch k := f.Kind(); k {
case 12:
fmt.Println(k) //12
case 0:
fmt.Println("Bye!")
}
}
英文:
Yes you are right, it is syntax error; it should be SimpleStmt or
ExprSwitchStmt = "switch" [ SimpleStmt ";" ] [ Expression ] "{" { ExprCaseClause } "}" .
see:
https://golang.org/ref/spec#Switch_statements
In an expression switch, the cases contain expressions that are compared against the value of the switch expression.
And this will work:
package main
import (
"fmt"
)
type Test struct {
kind int
}
func (s *Test) Kind() int {
return s.kind
}
func main() {
f := &Test{12}
//fmt.Println(k := f.Kind()) //syntax error: unexpected :=, expecting comma or )
switch k := f.Kind(); k {
case 12:
fmt.Println(k) //12
case 0:
fmt.Println("Bye!")
}
}
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