Golang Error packet usage and error type principle

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Package Mainimport ("Errors" "FMT") func F1 (code int) (int, error) {if code = = 1 {return-1, errors. New ("MSG test error")}return code, nil}type msgerror struct {code intmsg string}func f2 (code int) (int, error) {if code = = 1 {return-1, &msgerror{code, "struct MSG test Error"}}return code, Nil}//golang built-in error for interface type/* is defined as type err or interface {Error () string} can be found in the built-in package corresponding to the source code goroot/src/builtin/builtin.go specific How a situation does not understand. But look at the corresponding error in the package, the new method returns a corresponding constructor pointer and defines an error method guess should be if the return is the error type inside will automatically call the corresponding data type error method and so really understand again to modify the article * * Func (msg *msgerror) Error () string {return FMT. Sprintf ("%s", Msg. MSG)}func Main () {//for _, V: = range []int{1, 2, 3, 4, 5, 6} {//if code, ERR: = F1 (v); Err! = nil {//fmt. PRINTLN (ERR)//} else {//fmt. Println ("Success:", code)//}//}for _, I: = range []int{1, 2, 3} {if code, ERR: = F2 (i); Err! = Nil {fmt. Println (EXRR)} else {fmt. Println ("Success:", Code)}}