Maintenance of Ruby 2.0.0 ended on February 24, 2016. Read more
Weak Reference class that allows a referenced object to be garbage-collected.
A WeakRef may be used exactly like the object it references.
Usage:
foo = Object.new # create a new object instance p foo.to_s # original's class foo = WeakRef.new(foo) # reassign foo with WeakRef instance p foo.to_s # should be same class GC.start # start the garbage collector p foo.to_s # should raise exception (recycled)
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"=>#<Object:0x007f4ddfc6cb48>, "qux"=>"lol"} # 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.