class RDF::Util::Cache::ObjectSpaceCache

This implementation relies on ‘ObjectSpace#_id2ref` and performs optimally on Ruby >= 2.x; however, it does not work on JRuby by default since much `ObjectSpace` functionality on that platform is disabled unless the `-X+O` startup option is given.

@see ruby-doc.org/core-2.2.2/ObjectSpace.html @see ruby-doc.org/stdlib-2.2.0/libdoc/weakref/rdoc/WeakRef.html