UB in ListOf proxies

[Enchufa2]

Another UB triggered in

Rcpp/inst/tinytest/cpp/ListOf.cpp

Lines 108 to 110 in e5b03df

	CharacterVector listof_names(ListOf<NumericVector> x) {
	return x.names();
	}

The issue is in the definition

Rcpp/inst/include/Rcpp/vector/ListOf.h

Lines 25 to 30 in e5b03df

	template <typename T>
	class ListOf
	: public NamesProxyPolicy<T>
	, public AttributeProxyPolicy<T>
	, public RObjectMethods<T>
	{

Since ListOf<T> is a wrapper, it should inherit from NamesProxyPolicy<ListOf<T>> instead, etc. Otherwise, this cast produces the UB:

Rcpp/inst/include/Rcpp/proxy/NamesProxy.h

Lines 82 to 84 in e5b03df

	NamesProxy names() {
	return NamesProxy( static_cast<CLASS&>(*this) ) ;
	}

But then we need to avoid using methods that are not part of ListOf<T>, such as get__() and set__() (or define them). PR coming.