As for simultaneous writes, it would be nice if the class auto detected pins on the same port
The only purpose for my WriteMany class it to write like pins. A convenience factor is not really on my list at all.
imho a pingroup would have an internal collection to which runtime pins can be added and removed (don't know the purpose for remove yet)
The collection is not sorted, so the adding order applies.
Also pins probably should not be runtime, assigning runtime pins more than once doesn't really make sense unless you are physically re-wiring your hardware while the Arduino is on.
Also they are not usable values with digitalPin library and will have to resort to some slower lookup table version. making it more efficient to just individually write the pins.
Non-type template parameters also have no storage overhead, no SRAM is used to store the parameters past compilation as the compiled code is completely customised to those parameters. The alternative is a generic read/write that must look up the contents with every operation.
My code as tested for 3 and 4 pins produces less instructions on like pins rather than doing an individual write on each pin. When I finish the 4 & 5 pin writer I'll post it.
I'm not limiting this code to 8 pins though, The benefits my HAL will theoretically receive from writing any number of pins out ways this limitation by far.