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module Ref
# Implementation of a map in which only weakly referenced keys are kept to the map values.
# This allows the garbage collector to reclaim these objects if the only reference to them
# is the weak reference in the map.
#
# This is often useful for cache implementations since the map can be allowed to grow
# without bound and the garbage collector can be relied on to clean it up as necessary.
# One must be careful, though, when accessing entries since they can be collected at
# any time until there is a strong reference to the key.
#
# === Example usage:
#
# cache = Ref::WeakKeyMap.new
# obj = MyObject.find_by_whatever
# obj_info = Service.lookup_object_info(obj)
# cache[obj] = Service.lookup_object_info(obj)
# cache[obj] # The values looked up from the service
# obj = nil
# ObjectSpace.garbage_collect
# cache.keys # empty array since the keys and values have been reclaimed
#
# See AbstractReferenceKeyMap for details.
class WeakKeyMap < AbstractReferenceKeyMap
self.reference_class = WeakReference
end
end
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