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module Ref
# Implementation of a map in which weak references 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 the values can be collected
# at any time until there is a strong reference to them.
#
# === Example usage:
#
# cache = Ref::WeakValueMap.new
# foo = "foo"
# cache["strong"] = foo # add a value with a strong reference
# cache["weak"] = "bar" # add a value without a strong reference
# cache["strong"] # "foo"
# cache["weak"] # "bar"
# ObjectSpace.garbage_collect
# cache["strong"] # "foo"
# cache["weak"] # nil
#
# See AbstractReferenceValueMap for details.
class WeakValueMap < AbstractReferenceValueMap
self.reference_class = WeakReference
end
end
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