tree e98e57d22719817b526868aa13437c658221481e
parent 7e9340c8f6b17b629d235b34a434ac11b3184090
author Damien Neil <dneil@google.com> 1549908980 -0800
committer Damien Neil <dneil@google.com> 1549988619 +0000

design/29934-error-values.md: require that error be type assertable to As's target

Document As(err, target) as panicking when *target is not of interface
type and does not implement the error interface. While this prevents
some clever tricks, it permits catching (at runtime or statically
via vet) type errors equivalent to the ones that can be detected
by type assertions.

  if e := os.PathError{}; errors.As(err, &e) {  // error, os.PathError does not implement error
  if e := &os.PathError{}; errors.As(err, e) {  // error, os.PathError does not implement error
  if e := &os.PathError{}; errors.As(err, &e) { // ok

  var e interface{ Timeout() bool }
  if errors.As(&e) && e.Timeout() { // ok

Change-Id: Icfa8a1d4121601db458b1604fa57f6d1f38bc874
Reviewed-on: https://go-review.googlesource.com/c/161957
Reviewed-by: Jonathan Amsterdam <jba@google.com>