Is it defined to provide an inverted range to C++ standard algorithms?

Question

Consider standard algorithms like, say, std::for_each.

template
Function for_each(InputIterator first         


        

Answer 1

The standard defines complexity constraints for the functions taking ranges. In the specific case of for_each (25.2.4 in the C++ standard):

Complexity: Applies f exactly last - first times

So it's effectively a no-op in your example.