generic seralization api needs to be reworked

[cyrush]

To serialize / deserialize, the docs show we need to declare a zfp::array::header instance, however it is now an abstract class:

'zfp::array::header' is an abstract class
zfp::array::header header;

https://zfp.readthedocs.io/en/release1.0.0/arrays.html#serialization-1

For 1.0, the ZFP api changed to use concrete dimensioned types -- and this change undermined the generic seralization cases (using base zfp::array::header and zfp::array)

[lindstro]

As discussed offline, (de)serialization indeed appears broken. A possible workaround for serialization of a concrete array arr of type arr_type (e.g., zfp::array3<double>) is to use the derived type arr_type::header as header type, or (in C++11) decltype(arr)::header. If arr_type is the base class zfp::array, one likely would need a switch statement on arr.scalar_type() and arr.dimensionality() to determine the correct header type.

Deserialization is more challenging, as it requires first constructing a header object from a byte buffer; see constructor. However, the size of that buffer depends in principle on the header type being encoded in the buffer, which creates a chicken-and-egg problem. This is potentially a lesser problem if the header and compressed data have already been read into memory together, e.g., with the header immediately preceding the compressed data (as suggested by the serialization documentation).

It should be pointed out that the zfp CODEC header constructor performs various checks, e.g., to ensure that the optional bytes argument (i.e., the buffer size) matches the encoded header length and that the buffer stores a well-formed zfp header. If neither is true, an exception is raised. Upon successful construction, one can also interrogate the header for scalar type and dimensionality to choose a matching array class, e.g., in a switch statement.

This certainly is not what we had in mind when we redesigned zfp (de)serialization. This is a bug that will be addressed in a future release.