#079
Initial tests with [Boost].SML - a C++14 State Machine Library.
Notes
[Boost].SML is a C++14 State Machine Library delivered in a single header file with no dependencies.
It provides a pattern for defining events, guards and states. The transition table is described with an eUML style DSL.
Installation
It’s a single file:
wget https://raw.githubusercontent.com/boost-experimental/sml/master/include/boost/sml.hpp
Events Example
See events.cpp for a trivial example that experiments with the library. See the source for my annotations that clarify (read: helped me learn) how it fits together.
The output traces the state transitions (successful and failed):
$ make
c++ -std=c++17 -g -Wall -O3 events.cpp -o events
$ ./events
// create state machine with logger
// e2: ignored: e2 can't transition from initial idle state
[N12_GLOBAL__N_16eventsE][process_event] N12_GLOBAL__N_12e2E
// e1: transitions to s1
[N12_GLOBAL__N_16eventsE][process_event] N12_GLOBAL__N_12e1E
[N12_GLOBAL__N_16eventsE][transition] idle -> s1
// e2{false}: fails s1 to s2 guard condition
[N12_GLOBAL__N_16eventsE][process_event] N12_GLOBAL__N_12e2E
[N12_GLOBAL__N_16eventsE][guard] ZNK12_GLOBAL__N_16eventsclEvEUlRKNS_2e2EE_ N12_GLOBAL__N_12e2E [Reject]
// e2{}: passes s1 to s2 guard condition
[N12_GLOBAL__N_16eventsE][process_event] N12_GLOBAL__N_12e2E
[N12_GLOBAL__N_16eventsE][guard] ZNK12_GLOBAL__N_16eventsclEvEUlRKNS_2e2EE_ N12_GLOBAL__N_12e2E [OK]
[N12_GLOBAL__N_16eventsE][transition] s1 -> s2
// e3: on-the-fly event transitions from s2 to s3
[N12_GLOBAL__N_16eventsE][process_event] N5boost3sml6v1_1_03aux6stringIcJLc101ELc51EEEE
[N12_GLOBAL__N_16eventsE][transition] s2 -> s3
// e4{33}: fails s3 exit guard
[N12_GLOBAL__N_16eventsE][process_event] N12_GLOBAL__N_12e4E
[N12_GLOBAL__N_16eventsE][guard] ZNK12_GLOBAL__N_16eventsclEvEUlRKNS_2e4EE_ N12_GLOBAL__N_12e4E [Reject]
// e4{42}: spasses s3 guard and transitions to terminate state X
[N12_GLOBAL__N_16eventsE][process_event] N12_GLOBAL__N_12e4E
[N12_GLOBAL__N_16eventsE][guard] ZNK12_GLOBAL__N_16eventsclEvEUlRKNS_2e4EE_ N12_GLOBAL__N_12e4E [OK]
[N12_GLOBAL__N_16eventsE][transition] s3 -> terminate
[N12_GLOBAL__N_16eventsE][action] ZNK12_GLOBAL__N_16eventsclEvEUlRKT_E_ N12_GLOBAL__N_12e4E
// ignored - state machine has terminated
[N12_GLOBAL__N_16eventsE][process_event] N12_GLOBAL__N_12e4E
Credits and References
- [Boost].SML
- [Boost].SML - github