I think you should first look at numruby as it was part of this year's GSoC and ruby-sparse is very similar to it, so numruby's code will give you idea about how ruby-sparse is going to look in future. And you can find more details on ruby-sparse at https://github.com/Uditgulati/blog/wiki/Ruby-Grant-2019-proposal.
Thanks,
Udit Gulati