extending C++ class template (Boost++ state machines)

[PapaLegba]

This is probably extremely simple, but I am not comfortable with templates.

The Boost++ libraries define two templates which I wish to extend ...

template< class MostDerived,
class InitialState,
class Allocator = std::allocator< void >,
class ExceptionTranslator = null_exception_translator >
class state_machine : noncopyable
{};

template< class MostDerived,
class Context,
class InnerInitial = mpl::list<>,
history_mode historyMode = has_no_history >
class simple_state : public detail::simple_state_base_type< MostDerived,
typename Context::inner_context_type, InnerInitial >::type
{};

I would like to add a few more parameters, let's keep it simple and just start with a string which is state name or FSM name to use for debug tracing.

How do I extend these? And how do I declare an object of each of my new classes?

Thanks in advance for any help.

[weaknessforcats]

These templates are empty classes. And they are concrete (you can have objects of these classes).

You do not derive from concrete classes.

Do the Boost folks say what the purpose of the templates is?

[PapaLegba]

Well, the docs are on http://www.boost.org/doc/libs/1_36_0/libs/statechart/doc/index.html It all looks very good, but I'd like to add a few things. Just for starters, I'd like to pass a string giving the name of the state machine or state, which I can then use in debug tracing. When I get that working I can add more stuff.

I'd prefer to pass it in the constructor, rather than add a new method to set it, but I appear to be too dumb to do that :-(

[PapaLegba]

Well, I figure the extension ought to be

template< class fsmName, // Hint: pass a std::string
class MostDerived,
class InitialState,
class Allocator = std::allocator< void >,
class ExceptionTranslator = null_exception_translator >
class myFsm : public sc::state_machine <MostDerived, InitialState, Allocator, ExceptionTranslator>
{
};

template< class fsmStateName, // Hint: pass a std::string
class MostDerived,
class Context,
class InnerInitial = mpl::list<>,
history_mode historyMode = has_no_history >
class myFsmState : public sc::simple_state <MostDerived, Context>
{
};

Butt I can't figure out how to declare an object for a state machine and one for a state :-(

[weaknessforcats]

If you have a template, say line this:

template<class T, class U>
class MyClass
{
   T data;
   U data1;
 
};
 

You create objects by specializing the template. That is, you specify at compile time what the template will be converted into.

MyClass<string, int> obj;
MyClass<int, double> obj1;
 

There's no "passing to the contructor".

You do understand that the compiler makes a copy of the template and replaces the placeholders (like T and U) with the actual types and it is this copy that is compiled and used in your program?

If fsmStateName or fsmName are strings, then call out a string as the first parameter of your template.

myFsm<string, etc...> mystatemachine;
myFsmState<string, etc.....> mystate;