Are there cases where a typedef is absolutely necessary?

Question

Consider the following excerpt from the safe bool idiom:

typedef void (Testable::*bool_type)() const;
operator bool_type() const;

Is it possibl

Answer 1

In C++11, you can do it like this (gcc 4.5.2):

operator decltype((void (Testable::*)() const)(0))() const ;

I'm not saying it's pretty...