Missing default constructor for zfparray view

[harshithamenon]

In certain cases having a default constructor for the zfparray view class is helpful. For example, when the view is part of another object.

[lindstro]

A view should be thought of as a reference that generalizes single-element access to contiguous subarray access. Built-in references in C++ cannot be default initialized or reseated, nor is such functionality available for zfp's array::reference or STL's container references (though std::reference_wrapper supports this behavior). As far as I know, C++'s mdspan views of multidimensional arrays do not provide this capability either.

I'm not trying to make life more difficult for zfp users, but I wonder if this capability truly is needed. I'm also unsure what the API ought to look like. For instance, does assigning one view to another (which I believe would be needed to reseat the view) have value or reference semantics? Consider the analogous code snippet for references:

  type& a = b;
  a = c;

The assignment a = c actually copies the value of c to b (through the reference a) rather than reseat a to reference c. One way around this would be to provide a new function, e.g., a.rebind(c).

It would be beneficial to see examples where this functionality is needed as well as examples of APIs that provide such functionality.