[GitHub] [beam] youngoli commented on a change in pull request #11197: [BEAM-8292] Portable Reshuffle for Go SDK

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youngoli commented on a change in pull request #11197: [BEAM-8292] Portable Reshuffle for Go SDK
URL: https://github.com/apache/beam/pull/11197#discussion_r396823199
 
 

 ##########
 File path: sdks/go/pkg/beam/core/runtime/exec/coder.go
 ##########
 @@ -259,59 +298,82 @@ type customDecoder struct {
 	dec Decoder
 }
 
-func (c *customDecoder) Decode(r io.Reader) (*FullValue, error) {
+func (c *customDecoder) DecodeTo(r io.Reader, fv *FullValue) error {
 	// (1) Read length-prefixed encoded data
 
 	size, err := coder.DecodeVarInt(r)
 	if err != nil {
-		return nil, err
+		return err
 	}
 	data, err := ioutilx.ReadN(r, (int)(size))
 	if err != nil {
-		return nil, err
+		return err
 	}
 
 	// (2) Call decode
 
 	val, err := c.dec.Decode(c.t, data)
 	if err != nil {
+		return err
+	}
+	*fv = FullValue{Elm: val}
+	return err
 
 Review comment:
   I know this is just preserving the existing behavior, but it seems weird to `return err` here instead of `return nil`, even if it is guaranteed to be `nil` at this point.

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