anchor.diff:                  ctor, reader, fields, tags, picklers)
   
           let writer (w : WriteState) (_ : string) (u : 'Union) =
  -            let tag = tagReader.Invoke u
  +            let tag = tagReader u
               tagSerializer.WriteTag(w.Formatter, tag)
               let _,reader,_,tags,picklers = caseInfo.[tag]
               let values = reader u
  
positive.code:                 containsAttr<CustomEqualityAttribute> ty 
                  || containsAttr<ReferenceEqualityAttribute> ty
  
          // resolve tag reader methodInfo
          let tagReaderMethod =
              match FSharpValue.PreComputeUnionTagMemberInfo(ty, allMembers) with
  
negative.code:             ctor values |> fastUnbox<'Union>
  
          let cloner (c : CloneState) (u : 'Union) =
              let tag = tagReader u
              let ctor,reader,_,_,picklers = caseInfo.[tag]
              let values = reader u
              let values' = Array.zeroCreate<obj> values.Length
  