Passing template into boost function

Question

template <class EventType>
class IEvent;

class IEventable;

typedef boost::function<void (IEventable&, IEvent&)> behaviorRef;

What is the right way for passing template class IEvent into boost function? With this code I get: error: functional cast expression list treated as compound expression error: template argument 1 is invalid error: invalid type in declaration before ‘;’ token

Answer 1

boost::function needs a type, so you cannot pass it a template's name, it has to be a template instance. So either use a specific instance

typedef boost::function<void (IEventable&, IEvent<SomeEventType>&)> behaviorRef;

or put the whole thing itself into a template:

template< typename EventType >
struct foo {
  typedef boost::function<void (IEventable&, IEvent<EventType >&)> behaviorRef;
};

Answer 2

A class template is just a template for a class, it's not a real class yet. You need to specify the template parameters to get a class out of it, for example IEvent<int>. So you need to decide for which kind of events you want that typedef to be, for example for int:

typedef boost::function<void (IEventable&, IEvent<int>&)> behaviorRef;

Otherwise, if you want a typedef for all possible template instantiations, you need to put the typedef itself into another templated class. See sbi's answer for an example of that.