TGenCollectionProxy
 Proxy around an arbitrary container, which implements basic
 functionality and iteration. The purpose of this implementation
 is to shield any generated dictionary implementation from the
 underlying streamer/proxy implementation and only expose
 the creation fucntions.
 In particular this is used to implement splitting and abstract
 element access of any container. Access to compiled code is necessary
 to implement the abstract iteration sequence and functionality like
 size(), clear(), resize(). resize() may be a void operation.