Lucy::Store::Folder - Abstract class representing a directory.
# Abstract base class.
A "file" within a Folder might be a real file on disk -- or it might be a RAM buffer. Similarly, delete() might delete a file from the file system, or a key-value pair from a hash, or something else.
The archetypal implementation of Folder, FSFolder, represents a directory on the file system holding a collection of files.
Lucy::Store::Folder isa Lucy::Object::Obj.