Boost C++ Libraries: Ticket #9525: Assert with program termination due to context<...>() call in simple_state's entry action is incorrect

Andreas Huber — Tue, 31 Dec 2013 14:25:20 GMT

It's not correct to throw uncatchable surprises like asserts. It's especially incorrect when your library is used in the embedded software.

Not to mention this isn't reflected anywhere in the documentation.

Do you use std::vector? If yes, I'm wondering what you get when you dereference the return value of std::vector::end()? Last time I accidentally did that I got an assertion in DEBUG mode. I RELEASE mode, on most platforms dereferencing the return value of std::vector::end() does the wrong thing and return the contents of an invalid memory location. IIRC, the standard just says that the iterator you get from vector::end() must not be dereferenced.

I would argue that it's an almost identical situation with the simple_state::context() function. The reference docs say that you can't call this function in the constructor of a simple_state subclass:

<http://www.boost.org/doc/libs/1_55_0/libs/statechart/doc/reference.html#ClassTemplatesimple_state>

anonymous — Mon, 20 Jan 2014 13:18:21 GMT

It says "must not call", but it doesn't say *anything* about getting an assert and the program termination when you make a mistake (e.g. add context() call to a simple_state constructor but forget to change simple_state into state). Is this really the only way you can say "you've made a mistake" here?

anonymous — Sun, 26 Jan 2014 18:12:14 GMT

Replying to anonymous:

It says "must not call", but it doesn't say *anything* about getting an assert and the program termination when you make a mistake (e.g. add context() call to a simple_state constructor but forget to change simple_state into state).

IIRC, neither do the standard docs for std::vector::end.

Is this really the only way you can say "you've made a mistake" here?

The only other thing that comes to mind is throwing an exception, but exceptions have the problem that they can be ignored. Calling context() from a simple_state constructor makes the program broken beyond any hope of recovery. If you have any other suggestions, I'm all ears.