I would really like to specify the SBO size on boost::function! How about changing the signature to?: template class function; I've been trying to do a work around using the constructor with the allocator. I was going to define my own function class derived from the boost one, with a private one time allocator using a private buffer. This approach works find as long as constructors where the Functor type is present. The copy constructor and equals operators require serious hackery, since these constructors on boost function don't allow you to pass a new allow you to pass a new allocator. There's no template<typename Allocator> functionN(const functionN&, Allocator); This means that the Function constructor has to affect data underlying the const Function instance it's copying such that when the allocator is copied over it mutates into one that points at the private buffer of the new constructing instance. This is doable, but kind of scary since I'm making assumptions about when and how the Allocator is copied. This is also not such a wonderful solution, because the SBO is wasted. Any chance of just parameterizing the SBO size? Chris