Golang开关有一个`用作值`错误？

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

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!")
    }
}