type Version … const V0 … const V1 … const V2 … const numVersions … type Field … const Flags … const HasInit … const DerivedFuncInstance … const AliasTypeParamNames … const DerivedInfoNeeded … const numFields … var introduced … var removed … // Has reports whether field f is present in a bitstream at version v. func (v Version) Has(f Field) bool { … }