error 是接口类型：
// The error built-in interface type is the conventional interface for
// representing an error condition, with the nil value representing no error.
type error interface {
Error() string
}
只有两种创建error的方法：
- errors.New
- fmt.Errorf
Go 1.11: errors.New
package errors
// New returns an error that formats as the given text.
func New(text string) error {
return &errorString{text}
}
// errorString is a trivial implementation of error.
type errorString struct {
s string
}
func (e *errorString) Error() string {
return e.s
}
Go 1.11 fmt.Errorf():
// Errorf formats according to a format specifier and returns the string
// as a value that satisfies error.
func Errorf(format string, a ...interface{}) error {
return errors.New(Sprintf(format, a...))
}
来源：oschina
链接：https://my.oschina.net/renhc/blog/3212076