[boost] [result_of] result template in case of ambiguity

In the case that a function object is written where certain arguments may yield an ambiguous function call, how should the function object's result template be defined? Should using the result template emit an error upon instantiation, or should it merely not define the type typedef? I see different benefits and drawbacks for each approach and I'd rather not arbitrarily pick one if there is already an established convention for this case. -- -Matt Calabrese