The member operator
is overloaded to provide several ways to select
sequences of elements from among those controlled by *this.
Each of these
operations returns a subset of the array.
The const-qualified versions return this
subset as a new valarray
The non-const versions return a class
template object which has reference semantics to the original array, working in
conjunction with various overloads of operator=
and other assigning
operators to allow selective replacement (slicing) of the controlled sequence.
In each case the selected element(s) shall exist.