[GitHub] [beam] yyy1000 commented on a diff in pull request #25203: Fix interface{} in iter& emit type of DoFn in Go

["yyy1000 (via GitHub)" <gi...@apache.org>]

yyy1000 commented on code in PR #25203:
URL: https://github.com/apache/beam/pull/25203#discussion_r1089623120


##########
sdks/go/pkg/beam/core/funcx/output.go:
##########
@@ -84,6 +84,9 @@ func unfoldEmit(t reflect.Type) ([]reflect.Type, bool, error) {
 		if ok, err := isInParam(t.In(i)); !ok {
 			return nil, false, errors.Wrap(err, errIllegalParametersInEmit)
 		}
+		if t.In(i).Kind() == reflect.Interface || (t.In(i).Kind() == reflect.Pointer && t.In(i).Elem().Kind() == reflect.Interface) {

Review Comment:
   Thanks a lot! I'm clearer about this now.
   Does it mean we should not allow empty interfaces like "interface{}", but we do allow 'Universal Types'?
   But I still have a question is that, if a function has a param with "interface{}", like that
   ```
   Fn := func(interface{}){}
   t := reflect.TypeOf(Fn)
   ```
   but typex.ClassOf(t.In(0)) returns "Concrete", I ought to think it will return "Universal".
   The type system is a bit complex, I'm still learning it. :)
   



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