Base class for a cache. To use it you need to inherit it and override
getData method. It operates only on contiguous struct buffers and does
a copy of such buffer before returning cache element.
Boost Software License Version 1.0. See LICENSE_BOOST.txt for details.
Alternatively, this file may be distributed under the terms of the Tango
3-Clause BSD License (see LICENSE_BSD.txt for details).
Wraps a cache for struct values. When a record cannot be found in the cache, an abstract method is called to look up the record in an external source.