It probably better to call it UnaryFunction rather than UnaryFunctor as
unary functors already mean something more general in C++ (any functor
that takes one variable). I guess strictly speaking it should be
UnaryRealFunction, but we can get elide the Real.
Fair enough; as of r319 they are UnaryFunctions.
"It is a capital mistake to theorize before one has data."
- Sir Arthur Conan Doyle