Go函数返回nil遇到问题避坑分析

func returnsError() error {
	var p *MyError = nil
	if bad() {
		p = ErrBad
	}
	return p // Will always return a non-nil error.
}

func returnsError() error {
	if bad() {
		return ErrBad
	}
	return nil
}

type CustomError struct {
	Metadata map[string]string
	Message string
}
func (c CustomError) Error() string {
		return c.Message
}
var (
	ErrorA = CustomError{Message:"A", Matadata: map[string]string{"Reason":""}}
	ErrorB = CustomError{Message:"B"}
)
func DoSomething() error {
	return ErrorA
}

err:=DoSomething()
if errors.Is(err, ErrorA) {
	// handle err
}

func Is(err, target error) bool {
	if target == nil {
		return err == target
	}
	isComparable := reflect.TypeOf(target).Comparable()
	for {
		if isComparable && err == target {
			return true
		}
		if x, ok := err.(interface{ Is(error) bool }); ok && x.Is(target) {
			return true
		}
		if err = errors.Unwrap(err); err == nil {
			return false
		}
	}
}

var (
	ErrorA = &CustomError{Message:"A", Matadata: map[string]string{"Reason":""}}
	ErrorB = &CustomError{Message:"B"}
)