In our project, we need a generic interface to refer to different state machine (back-end). For example, in the following codes, we want
to use SMBase* to refer to any concrete state machine. SMBase should have similar interface as state machine.
struct User { A(SMBase* s) : sm(s) (); SMBase* sm; ... // User can use sm->start(), sm->process_event() etc }
struct SMBase { virtual void start() = 0; ... // how to design the rest ??? }
The problem of designing SMBase is the function "process_event". We want it to to be virtual function so SMWrapper can implement it. >But it also needs to be a template according to state machine interface. But we cannot have a virtual template function.
How can we achieve/design this generic state machine interface?
Hi Jerry, Yes, virtual template methods are not possible in C++ :( (Note to C++ Standard Comittee: I'd consider donating a kidney for this one :) ) This leaves you with few possibilies. I see 2 at a first glance (suggestions welcome): - virtual void process_event_event1(); virtual void process_event_event2(); ...etc (not fun but quite in the OO spirit) - virtual void process_event(boost::any) followed by any_casts until you find the correct one (not fun either) All considered, solution 1 looks better. If you can define a common interface for state machines, then they are bound to expect common events. HTH, Christophe