Make `RecordCache` work on a single record only, and implement a mapping from
field names (only) to values.
Also add explicit methods on `RecordCache` to wrap special behavior in cache,
and simplify all special values as a wrapper for a getter function.
The record cache may contain regular and special values. Modify `RecordCache`
so that only methods ending with `_value` check for regular values. The
dictionary methods considers both regular and special values as equivalent.
name in record._cache # test if cache has a value
iter(record._cache) # iterate on values
record._cache[name] # get value
record._cache.get(name) # get value or default
record._cache.has_value(name) # test if cache has a regular value
record._cache.get_value(name) # get regular value or default
Raphael Collet
64e945aa44