diff --git a/ChangeLog b/ChangeLog index 3734eb3b46..0b2e53e1e9 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,8 @@ +Sun Dec 2 16:48:00 2012 Zachary Scott + + * lib/weakref.rb (rdoc): Clean up usage, add example, + note ArgumentError on WeakRef.new + Sun Dec 2 16:45:00 2012 Zachary Scott * gc.c (WeakMap): Add doc for internal reference, use lib/weakref.rb diff --git a/lib/weakref.rb b/lib/weakref.rb index 78f88a3f12..0689efadec 100644 --- a/lib/weakref.rb +++ b/lib/weakref.rb @@ -1,18 +1,66 @@ require "delegate" # Weak Reference class that allows a referenced object to be -# garbage-collected. A WeakRef may be used exactly like the object it -# references. +# garbage-collected. +# +# A WeakRef may be used exactly like the object it references. # # Usage: # -# foo = Object.new -# foo = Object.new +# foo = Object.new # create a new object instance # p foo.to_s # original's class -# foo = WeakRef.new(foo) +# foo = WeakRef.new(foo) # reassign foo with WeakRef instance # p foo.to_s # should be same class -# ObjectSpace.garbage_collect +# GC.start # start the garbage collector # p foo.to_s # should raise exception (recycled) +# +# == Example +# +# With help from WeakRef, we can implement our own redimentary WeakHash class. +# +# We will call it WeakHash, since it's really just a Hash except all of it's +# keys and values can be garbage collected. +# +# require 'weakref' +# +# class WeakHash < Hash +# def []= key, obj +# super WeakRef.new(key), WeakRef.new(obj) +# end +# end +# +# This is just a simple implementation, we've opened the Hash class and changed +# Hash#store to create a new WeakRef object with +key+ and +obj+ parameters +# before passing them as our key-value pair to the hash. +# +# With this you will have to limit your self to String key's, otherwise you +# will get an ArgumentError because WeakRef cannot create a finalizer for a +# Symbol. Symbols are immutable and cannot be garbage collected. +# +# Let's see it in action: +# +# omg = "lol" +# c = WeakHash.new +# c['foo'] = "bar" +# c['baz'] = Object.new +# c['qux'] = omg +# puts c.inspect +# #=> {"foo"=>"bar", "baz"=>#, "qux"=>"omg"} +# +# # Now run the garbage collector +# GC.start +# c['foo'] #=> nil +# c['baz'] #=> nil +# c['qux'] #=> nil +# omg #=> "lol" +# +# puts c.inspect +# #=> WeakRef::RefError: Invalid Reference - probably recycled +# +# You can see the local variable +omg+ stayed, although it's reference in our +# hash object was garbage collected, along with the rest of the keys and +# values. Also, when we tried to inspect our hash, we got a WeakRef::RefError, +# this is because these objects were also garbage collected. class WeakRef < Delegator @@ -27,6 +75,9 @@ class WeakRef < Delegator ## # Creates a weak reference to +orig+ + # + # Raises an ArgumentError if the given +orig+ is immutable, such as Symbol, + # Fixnum, or Float. def initialize(orig) case orig