-/* Buffering shim for implementing clone and peek operations.
-
- The "clone" and "peek" operations aren't implemented by all
- types of casereaders, but we have to expose a uniform
- interface anyhow. We do this by interposing a buffering
- casereader on top of the existing casereader on the first call
- to "clone" or "peek". The buffering casereader maintains a
- window of cases that spans the positions of the original
- casereader and all of its clones (the "clone set"), from the
- position of the casereader that has read the fewest cases to
- the position of the casereader that has read the most.
-
- Thus, if all of the casereaders in the clone set are at
- approximately the same position, only a few cases are buffered
- and there is little inefficiency. If, on the other hand, one
- casereader is not used to read any cases at all, but another
- one is used to read all of the cases, the entire contents of
- the casereader is copied into the buffer. This still might
- not be so inefficient, given that case data in memory is
- shared across multiple identical copies, but in the worst case
- the window implementation will write cases to disk instead of
- maintaining them in-memory. */
-
-/* A buffering shim for a non-clonable or non-peekable
- casereader. */
-struct shim
- {
- struct casewindow *window; /* Window of buffered cases. */
- struct casereader *subreader; /* Subordinate casereader. */
- };
-
-static const struct casereader_random_class shim_class;