line to tutorials/dataframe/df012_DefinesAndFiltersAsStrings.C and
$ root -q df012_DefinesAndFiltersAsStrings.C
Processing df012_DefinesAndFiltersAsStrings.C...
Error in <TBranchElement::InitializeOffsets>: Could not find the real data member '_M_elems[2]' when constructing the branch 'p' [Likely missing ShowMember].
I’ve thought ROOT has built-in support for STL collections.
I don’t think root treats yet std::arrays as stl containers. They can be used as data members and transparent schema evo is guaranteed wrt fixed size C arrays. on the other hand something is still missing for the usage of such containers as top level branches i believe…
for writing: detect the type fed to the branch (with c++ or root typesystem) and if std array, create a plain fixed size array branch
for reading: just take the address of the first element of the stl array and read into it as if it were a C array.
the hairy part could eventually be the treatment of nested arrays maybe…