[GitHub] [beam] youngoli commented on a change in pull request #10991: [BEAM-3301] Refactor DoFn validation & allow specifying main inputs.

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youngoli commented on a change in pull request #10991: [BEAM-3301] Refactor DoFn validation & allow specifying main inputs.
URL: https://github.com/apache/beam/pull/10991#discussion_r388089313
 
 

 ##########
 File path: sdks/go/pkg/beam/core/graph/fn.go
 ##########
 @@ -209,21 +209,58 @@ func (f *DoFn) RestrictionT() *reflect.Type {
 // a KV or not based on the other signatures (unless we're more loose about which
 // sideinputs are present). Bind should respect that.
 
+// Constants so we can avoid magic numbers in validation. Represent number of
+// DoFn main inputs based on what kind of input the DoFn has.
+const (
+	unknownInNum = -1 // Used when we don't know the number of main inputs.
+	singleInNum  = 1
+	kvInNum      = 2
+)
+
 // NewDoFn constructs a DoFn from the given value, if possible.
 func NewDoFn(fn interface{}) (*DoFn, error) {
 	ret, err := NewFn(fn)
 	if err != nil {
 		return nil, errors.WithContext(errors.Wrapf(err, "invalid DoFn"), "constructing DoFn")
 	}
-	return AsDoFn(ret)
+	return AsDoFn(ret, unknownInNum)
 }
 
-// AsDoFn converts a Fn to a DoFn, if possible.
-func AsDoFn(fn *Fn) (*DoFn, error) {
+// NewDoFnKv constructs a DoFn from the given value, if possible, with
+// improved validation from knowing whether the DoFn's main input is a KV or
+// single element.
+func NewDoFnKv(fn interface{}, mainKv bool) (*DoFn, error) {
 
 Review comment:
   Done, went with the variadic options made of functions approach. If anyone else is reading this, based it off this article: https://dave.cheney.net/2014/10/17/functional-options-for-friendly-apis

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