Interesting, so maybe a feasible path to achieve this while keeping code extensible would be to use a macro as in Macro to write function with many conditionals - #8 by Skoffer, and then add a mechanism to reload all functions that depend on the subtypes output if a new subtype has been added, effectively just overwriting the old version. I think that would give you both optimal speed, low allocations, and would allow others to add new subtypes after the fact.