Class: WeakRef
Relationships & Source Files | |
Namespace Children | |
Exceptions:
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Super Chains via Extension / Inclusion / Inheritance | |
Class Chain:
self,
Delegator
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Instance Chain:
self,
Delegator
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Inherits: |
Delegator
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Defined in: | lib/weakref.rb |
Overview
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)
Example
With help from WeakRef
, we can implement our own rudimentary 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 keys, 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 its 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 RefError. This is because these objects were also garbage collected.
Class Method Summary
-
.new(orig) ⇒ WeakRef
constructor
Creates a weak reference to
orig
Instance Attribute Summary
-
#weakref_alive? ⇒ Boolean
readonly
Returns true if the referenced object is still alive.
Constructor Details
.new(orig) ⇒ WeakRef
Creates a weak reference to orig
Raises an ArgumentError if the given orig
is immutable, such as Symbol, Fixnum, or Float.
# File 'lib/weakref.rb', line 83
def initialize(orig) case orig when true, false, nil @delegate_sd_obj = orig else @@__map[self] = orig end super end
Instance Attribute Details
#weakref_alive? ⇒ Boolean
(readonly)
Returns true if the referenced object is still alive.
# File 'lib/weakref.rb', line 104
def weakref_alive? @@__map.key?(self) or defined?(@delegate_sd_obj) end