groot/rdict: leverage rbytes.{Unm,M}arshaler implementation in Bind

This CL adds a temporary mitigation of #880.
It tries to detect whether a given receiver for binding implements rbytes.Unmarshaler and
use it instead of generating rstreamers.

rstreamers may not properly work in the case where fields of a struct aren't exported.

Fixes #880.

groot/rdict/decoder.go

@@ -84,6 +84,16 @@ func (rr *rstreamerInfo) Bind(recv interface{}) error {
 		return fmt.Errorf("rdict: invalid kind (got=%T, want=pointer)", recv)
 	}
 	rr.recv = recv
+	if recv, ok := recv.(rbytes.Unmarshaler); ok && rr.kind == rbytes.ObjectWise {
+		// FIXME(sbinet): handle mbr-/obj-wise
+		rr.rops = []rstreamer{{
+			op: func(r *rbytes.RBuffer, _ interface{}, _ *streamerConfig) error {
+				return recv.UnmarshalROOT(r)
+			},
+			cfg: nil,
+		}}
+		return nil
+	}
 	if len(rr.rops) == 1 {
 		se := rr.rops[0].cfg.descr.elem
 		if se.Name() == "This" ||

groot/rdict/encoder.go

@@ -75,6 +75,16 @@ func (ww *wstreamerInfo) Bind(recv interface{}) error {
 		return fmt.Errorf("rdict: invalid kind (got=%T, want=pointer)", recv)
 	}
 	ww.recv = recv
+	if recv, ok := recv.(rbytes.Marshaler); ok && ww.kind == rbytes.ObjectWise {
+		// FIXME(sbinet): handle mbr-/obj-wise
+		ww.wops = []wstreamer{{
+			op: func(w *rbytes.WBuffer, _ interface{}, _ *streamerConfig) (int, error) {
+				return recv.MarshalROOT(w)
+			},
+			cfg: nil,
+		}}
+		return nil
+	}
 	if len(ww.wops) == 1 && ww.wops[0].cfg.descr.elem.Name() == "This" {
 		// binding directly to 'recv'. assume no offset is to be applied
 		ww.wops[0].cfg.offset = -1

groot/rdict/rdict.go

@@ -219,6 +219,9 @@ func (si *StreamerInfo) build(sictx rbytes.StreamerInfoContext) error {
 	for i, descr := range si.descr {
 		si.roops = append(si.roops, si.makeROp(sictx, i, descr))
 		si.woops = append(si.woops, si.makeWOp(sictx, i, descr))
+		// FIXME(sbinet): handle member-wise r/w ops
+		// si.rmops
+		// si.wmops
 	}
 
 	return nil