Clients need both the message and the rexp.proto descriptor to parse
serialized R objects. The latter is included in the the package installation
proto directory: system.file(package="RProtoBuf", "proto/rexp.proto")
The following storage types are natively supported by the descriptor:
character, raw, double, complex, integer,
list, and NULL. Objects with other storage types, such as
functions, environments, S4 classes, etc, are serialized using base R
serialize and stored in the proto native type.
Missing values, attributes and numeric precision will be preserved.