Boost.Function optimization for stateless function objects

From: Douglas Gregor (gregod_at_[hidden])
Date: 2002-01-29 22:35:58

I've just committed some changes to Boost.Function so that it will optimize 
away unnecessary allocations and copying of stateless function objects. Thus, 
construction of or assignment to a Boost.Function object given a stateless 
function object will not throw, and will not allocate any memory.

To do this, a new type trait, is_stateless, has been added to 
boost/type_traits/object_traits.hpp. The definition of is_stateless is:

template <typename T>
struct is_stateless
{
  BOOST_STATIC_CONSTANT(bool, value = 
    (::boost::type_traits::ice_and<
       ::boost::has_trivial_constructor<T>::value,
       ::boost::has_trivial_copy<T>::value,
       ::boost::has_trivial_destructor<T>::value,
       ::boost::is_class<T>::value,
       ::boost::is_empty<T>::value
     >::value));
};

The functionality has been tested under GCC, Comeau, and MSVC without any 
problems. Documentation may lag behind a bit, but I'm working on it.

Comments always welcome.

        Doug