我正在檢查 Go v1.13 Go v1.14 中的錯誤跟蹤。為什么似乎只能找到沒有參數或帶有值接收器的錯誤實現errors.Is()？這意味著能夠包裝的錯誤實現必須有一個值接收器才能被errors.Is().package mainimport ( "fmt" "errors")type someAtomicError struct {}func (e *someAtomicError) Error() string { return "Hi!" }func checkAtomicError() { e := &someAtomicError{} e2 := fmt.Errorf("whoa!: %w", e) e2IsE := errors.Is(e2, &someAtomicError{}) fmt.Println("atomic error trace ---\t\t", e2, "\t\t--- is traceable: ", e2IsE)}type someWrapperError struct { Msg string Err error}func (e someWrapperError) Error() string { return fmt.Sprintf("%s: %v", e.Msg, e.Err) }func (e someWrapperError) Unwrap() error { return e.Err }func checkWrapperError() { e := someWrapperError{"Hi!", nil} e2 := fmt.Errorf("whoa!: %w", e) e2IsE := errors.Is(e2, someWrapperError{"Hi!", nil}) fmt.Println("wrapper error trace ---\t\t", e2, "\t--- is traceable: ", e2IsE)}type somePointerWrapperError struct { Msg string Err error}func (e *somePointerWrapperError) Error() string { return fmt.Sprintf("%s: %v", e.Msg, e.Err) }func (e *somePointerWrapperError) Unwrap() error { return e.Err }func checkPointerWrapperError() { e := &somePointerWrapperError{"Hi!", nil} e2 := fmt.Errorf("whoa!: %w", e) e2IsE := errors.Is(e2, &somePointerWrapperError{"Hi!", nil}) fmt.Println("pointer wrapper error trace ---\t", e2, "\t--- is traceable: ", e2IsE)}func main() { checkAtomicError() checkWrapperError() checkPointerWrapperError()}//atomic error trace --- whoa!: Hi! --- is traceable: true//wrapper error trace --- whoa!: Hi!: <nil> --- is traceable: true//pointer wrapper error trace --- whoa!: Hi!: <nil> --- is traceable: falsehttps://play.golang.org/p/-hSukZ-gii2似乎參數的任何差異，包括包裝的錯誤參數，Err都會導致無法找到類型errors.Is()。
2 回答
qq_笑_17
TA貢獻1818條經驗 獲得超7個贊
false您在嘗試在另一個通過中查找一個錯誤時得到的原因errors.Is是因為 - 雖然這兩個錯誤可能具有相同的字段值 - 它們是兩個不同的內存指針：
e := &somePointerWrapperError{"Hi!", nil}
e2 := &somePointerWrapperError{"Hi!", nil} // e2 != e
ew := fmt.Errorf("whoa!: %w", e)
errors.Is(ew, e) // true
errors.Is(ew, e2) // false - because `ew` wraps `e` not `e2`
那么如何檢測這種“類型”的錯誤并獲取它的值：errors.As改用：
e := &somePointerWrapperError{"Hi!", nil}
e2 := fmt.Errorf("whoa!: %w", e)
var ev *somePointerWrapperError
if errors.As(e2, &ev) {
fmt.Printf("%#v\n", ev) // &somePointerWrapperError{Msg:"Hi!", Err:error(nil)}
}
https://play.golang.org/p/CttKThLasXD
泛舟湖上清波郎朗
TA貢獻1818條經驗 獲得超3個贊
遠程相關，但可能對某人有所幫助：我花了一些時間才意識到errors.As(...)實際上需要一個指向目標的雙指針，而errors.Is(...)沒有：
var _ error = (*CustomError)(nil) // ensure CustomError implements error
type CustomError struct {
msg string
}
func (e CustomError) Error() string {
return e.msg
}
func main() {
err := &CustomError{"Hello, world!"} // Methods return pointers to errors, allowing them to be nil
var eval *CustomError
as := errors.As(err, &eval) // yes, that's **CustomError
asFaulty := errors.As(err, eval) // no compile error, so it wrongly seems okay
is := errors.Is(err, eval) // that's just *CustomError
fmt.Printf("as: %t, asFaulty: %t, is: %t", as, asFaulty, is) // as: true, asFaulty: false, is: true
}
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