Arity of a generic lambda

Question

It is possible to deduce arity of a non-generic lambda by accessing its operator().

template 
struct fInfo : fInfo

        

Answer 1

It's impossible, as the function call operator can be a variadic template. It's been impossible to do this forever for function objects in general, and special-casing lambdas because they happened to not be equally powerful was always going to be a bad idea. Now it's just time for that bad idea to come home to roost.