HFSM2 VS hsm

Here is a gist showing a 3 level hierarchy using sml. https://gist.github.com/indiosmo/08ab24181770125d5a2448d27f6ae99f. Comparing the two, esp. when anything related to *hierarchical* state machines are involved, I strongly prefer HFSM2. Even when comparing the source code, I prefer HFSM2 https://github.com/andrew-gresyk/HFSM2/blob/master/include/hfsm2/machine.hpp to boost::sml https://github.com/boost-ext/sml/blob/master/include/boost/sml.hpp.

Finally you can make a more complete Hierarchical (or Nested) State Machine, which allows you to have states within states. This is what we've done in several games I've worked on. This can allow reusing states in multiple contexts, such as being in an Idle state that pushes a Targeting state, or in a Running state that also pushes the Targeting state. You are then considered in all of the states on your state stack. This is tricky to implement right though and needs careful design, but used correctly can be extremely powerful. I'm aware of a C++ HSM library that I can recommend ( https://github.com/amaiorano/hsm ), but there's probably other good ones out there.