// +build go1.13 package errors import (	stderrors "errors") // Is reports whether any error in err's chain matches target.//// The chain consists of err itself followed by the sequence of errors obtained by// repeatedly calling Unwrap.//// An error is considered to match a target if it is equal to that target or if// it implements a method Is(error) bool such that Is(target) returns true.func Is(err, target error) bool { return stderrors.Is(err, target) } // As finds the first error in err's chain that matches target, and if so, sets// target to that error value and returns true.//// The chain consists of err itself followed by the sequence of errors obtained by// repeatedly calling Unwrap.//// An error matches target if the error's concrete value is assignable to the value// pointed to by target, or if the error has a method As(interface{}) bool such that// As(target) returns true. In the latter case, the As method is responsible for// setting target.//// As will panic if target is not a non-nil pointer to either a type that implements// error, or to any interface type. As returns false if err is nil.func As(err error, target interface{}) bool { return stderrors.As(err, target) } // Unwrap returns the result of calling the Unwrap method on err, if err's// type contains an Unwrap method returning error.// Otherwise, Unwrap returns nil.func Unwrap(err error) error {	return stderrors.Unwrap(err)}