LGTM! Especially given loops.h.src still works in C++ and also uses the .c.src templating.

Actually doing a C++ conversion on arraytypes.h to use e.g. template functions will also require converting item_selection.c and multiarraymodule.c which will probably not happen for a while, so we probably won't be able to replace the .c.src templating in the header here.

Planned: Convert argfunc.dispatch.c.src to argfunc.dispatch.cpp to enable C++ language features and improve code maintainability.

Nice! That seems like a good isolated choice to start with.