[boost] [type_traits] Why is there no total extent?

I was wondering why there is no total_extent in the TypeTraits library. total_extent would represent the total number of elements in a complete built-in array type, else it would be zero. I would think that this would be a natural supplement to the existing extent metafunction. (There is a very similar functionality in the smart pointers library, under the name of array_total here: smart_ptr/detail/array_traits.hpp) Mostafa