Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

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Frontend / Backend interface

The design of MSM tries to make front-ends and back-ends (later) to be as interchangeable as possible. Of course, no back-end will ever implement every feature defined by any possible front-end and inversely, but the goal is to make it as easy as possible to extend the current state of the library.

To achieve this, MSM divides the functionality between both sides: the front-end is a sort of user interface and is descriptive, the back-end implements the state machine engine.

MSM being based on a transition table, a concrete state machine (or a given front-end) must provide a transition_table. This transition table must be made of rows. And each row must tell what kind of transition it is and implement the calls to the actions and guards. A state machine must also define its regions (marked by initial states) And that is about the only constraints for front-ends. How the rows are described is implementer's choice.

Every row must provide:

Furthermore, a front-end must provide the definition of states and state machines. State machine definitions must provide (the implementer is free to provide it or let it be done by every concrete state machine. Different MSM front-ends took one or the other approach):

States and state machines must both provide a (possibly empty) definition of: