# Programming Ruby ### The Pragmatic Programmer's Guide
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module ObjectSpace

### Index:

_id2ref define_finalizer each_object garbage_collect undefine_finalizer

The `ObjectSpace` module contains a number of routines that interact with the garbage collection facility and allow you to traverse all living objects with an iterator.

`ObjectSpace` also provides support for object finalizers, procs that will be called when a specific object is about to be destroyed by garbage collection.

    include ObjectSpace

    a = "A"
    b = "B"
    c = "C"

    define_finalizer(a, proc {|id| puts "Finalizer one on #{id}" })
    define_finalizer(a, proc {|id| puts "Finalizer two on #{id}" })
    define_finalizer(b, proc {|id| puts "Finalizer three on #{id}" })

produces:

    Finalizer three on 537767360
    Finalizer one on 537767510
    Finalizer two on 537767510

class methods
_id2ref | ObjectSpace._id2ref( anId ) -> anObject
|  | Converts an object id to a reference to the object. May not be called on an object id passed as a parameter to a finalizer.
`s = "I am a string"` | » | `"I am a string"`
`r = ObjectSpace._id2ref(s.id)` | » | `"I am a string"`
`r == s` | » | `true`
define_finalizer | ObjectSpace.define_finalizer( anObject, aProc=proc() )
|  | Adds aProc as a finalizer, to be called when anObject is about to be destroyed.
each_object | ObjectSpace.each_object( [ aClassOrMod ] ) {| anObj | block } -> aFixnum
|  | Calls the block once for each living, nonimmediate object in this Ruby process. If aClassOrMod is specified, calls the block for only those classes or modules that match (or are a subclass of) aClassOrMod. Returns the number of objects found.
    a = 102.7
    b = 95
    ObjectSpace.each_object(Numeric) {|x| p x }
    print "Total count: ", ObjectSpace.each_object {} ,"\n"
produces:
    102.7
    2.718281828
    3.141592654
    Total count: 372
garbage_collect | ObjectSpace.garbage_collect -> `nil`
|  | Initiates garbage collection (see module `GC` on page 410).
undefine_finalizer | ObjectSpace.undefine_finalizer( anObject )
|  | Removes all finalizers for anObject.

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Extracted from the book "Programming Ruby - The Pragmatic Programmer's Guide"
Copyright © 2001 by Addison Wesley Longman, Inc. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at http://www.opencontent.org/openpub/)).

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