I have used and watched closely this library for more than a year, since its early versions. Initially, we needed a good modern state machine framework for a project at the company I work for. After evaluating the possibilities, we decided to take the risk and go with Andreas' FSM, despite its early-alpha state at the time. Now, one year later, that choice has proved to be correct. We have used FSM in one more project and are planning to use it in future projects too. * What is your evaluation of the documentation? How easy (or hard) it is to understand library features? What can be improved? The documentation is very adequate. I was able to quickly understand how to use the basic features of the library, and then proceed to the advanced ones. At that time I had experience with different kinds of state machines, but primarily SDL-specified. FSM's documentation was my first introduction to UML state charts, and did the job well. The tutorial is excellent. The FAQ and Rationale sections give important answers to questions which are likely to arise. There is also an extensive Reference section, which I needed very rarely. * What is your evaluation of the design? What features are supported better by alternative FSMs? What could be added (or removed) from the library? To me, the design is good and follows naturally from the objectives of the library. It imposes some restrictions, although they can be overcome if necessary (for me it has not been necessary). For example, machines don't recognize polymorphic events, therefore they cannot "forward" unknown events to another machine. This can be circumvented by using a "wrapper" event around such events, which works, but only with asynchronous machines. Another example is the way that state machines are inherited - it's not very flexible and only allows altering how a state machine reacts to an already recognized event. One cannot add support for new events, except using again the "wrapper event" trick. * The library documentation contains few not yet solved issues (name, separating the library into two parts, exception handling). What is you opinion here? The name (boost::fsm, Boost.FSM) is fine for me. Regarding separating the library into two parts, I prefer it being separated, since the Worker part is useful by itself. * What is your evaluation of the implementation? Are there parts of code too obscure or duplicating exiting Boost functionality? Can something be factored out to standalone library or among general utilities? It's as obscure as its complexity requires. At the same time it is stable and bug-free, which is proved by extensive bulk-testing in our labs. * Are there performance bottlenecks? Does the library design fit requirements of real-time systems? How is it usable for embedded systems? Is the documentation clear on performance tradeoffs? The documentation is definitely clear on performance tradeoffs, and it's up to the potential user to take an informed decision. One tradeoff is that dispatch time is linear to the number of nested states. In my experience this is not a problem, since there are rarely more than two nested states, and I have never seen more than three. A possible problem is that states are constructed using operator new(). The documentation clearly states that, and the library allows overcoming the issue by specifying a custom allocator for the state machine, as well as writing custom operator new()'s for all state classes. I personally am against the second requirement and think that it complicates things too much. Specifying a custom allocator for the state machine should be enough. (this is mentioned in the documentation, in the Rationale section under "Memory management customization") * What is your evaluation of the potential usefulness of the library? Can you compare this FSM to other implementations? The greatest distinction of code written using the FSM library is its manageability. It's very easy to write and subsequently evolve state machines and most common mistakes are caught at compilation time. When state machines are involved, using FSM is definitely a great improvement over using a primitive framework, or not using a framework at all (the notorious switch/case idiom). Especially if the library's advanced features are used. * Did you try to use the library? With what compiler? Did you have any problems? Do you have tips for better support of older compilers? What are possible portability problems? Used with MSVC++ 7.1 and GCC 3.x. Currently without problems. In the early versions there were some minor issues which Andreas has addressed quickly. Regarding older compilers, I don't think they should be supported by this library. * How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? In-depth study, as well as real-world usage. * Are you knowledgeable about the problem domain? To a good extent. I have developed two different state machine frameworks, although both of them were significantly lower level than FSM. I have also worked extensively with various kinds of state machines, mainly protocol-related and in telecom applications. * Do you think the library should be accepted as a Boost library? Be sure to say this explicitly so that your other comments don't obscure your overall opinion. Yes. Definitely.