> I assumed mutable (implicit) state was being argued in favour of an explicit state representation.
I definitely was not: I would argue for structured logic rather than implicit state. The idea you are discussing seems to be more about imperative vs. functional design, and that would also be a lot better... but these are Google engineers managing a million interacting state machines via a giant pile of global (mutable) state, resulting in tons of bugs such as this one that isn't even fixed yet:
https://issues.webrtc.org/issues/339131894
A reply I just left elsewhere on this thread, noting that "state machine" doesn't imply the clean perfectly-factored concept you'd learn in a computer science class: these are ad hoc state machines that result from having a number of developers who don't really care and who think they can "dead reckon" the state of the system if they just add enough transition functions.
> these are Google engineers managing a million interacting state machines via a giant pile of global (mutable) state
Yeah that doesn't sound good. I understand the point you are making now and agree.