There are some worries that MSM generates huge code. Is it true? The 2 compilers I tested disagree with this claim. On VC9, the test state machines used in the performance section produce executables of 14kB (for simple and eUML) and 21kB (for the composite). This includes the test code and iostreams. By comparison, an empty executable with iostreams generated by VC9 has a size of 7kB. Boost.Statechart generates executables of 43kB and 54kB. As a bonus, eUML comes for “free” in terms of executable size. You even get a speed gain. With g++ 4.3, it strongly depends on the compiler options (much more than VC). A good size state machine with –O3 can generate an executable of 600kB, and with eUML you can get to 1.5MB. Trying with –Os –s I come down to 18kB and 30kB for the test state machines, while eUML will go down to 1MB (which is still big), so in this case eUML does not come for free.