# How to do explicit copy **URL:** \ **Category:** Ruby\ **Created:** [October 6, 2009, 5:45pm UTC](https://www.ruby-forum.com/t/how-to-do-explicit-copy/176819 "2009-10-06T17:45:48Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![rickyr](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ed655f/32.png) [@rickyr](https://www.ruby-forum.com/u/rickyr)\ **Post date:** [October 6, 2009, 5:45pm UTC](https://www.ruby-forum.com/t/how-to-do-explicit-copy/176819/1 "2009-10-06T17:45:48Z")
Hi, I notice Ruby uses reference copy by default. The problem is I need to keep two variables keep separate copies of the same data. If I do this: x = Hash.new # fill a with data y = x # delete some keys from x I got those same keys deleted from y ('cos x & y reference the same data, I believe). How to tell ruby that I want y keep a separate copy of x’s data, so that if I do anything to x, y is not effected. TIA ---
**Author:** ![rickyr](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ed655f/32.png) [@rickyr](https://www.ruby-forum.com/u/rickyr)\ **Post date:** [October 6, 2009, 5:51pm UTC](https://www.ruby-forum.com/t/how-to-do-explicit-copy/176819/2 "2009-10-06T17:51:40Z")
On Oct 6, 2009, at 6:45 PM, rickyr wrote: > y = x y = x.dup may be sufficient for you (it does a shallow copy). ---
**Author:** ![rickyr](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ed655f/32.png) [@rickyr](https://www.ruby-forum.com/u/rickyr)\ **Post date:** [October 8, 2009, 5:56am UTC](https://www.ruby-forum.com/t/how-to-do-explicit-copy/176819/3 "2009-10-08T05:56:03Z")
On Oct 6, 10:50 pm, Patrick O. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > On Oct 6, 2009, at 6:45 PM, rickyr wrote: > > > y = x > > y = x.dup may be sufficient for you (it does a shallowcopy). > > – > patrick Thanks, it worked. Now, what are the differences between object#dup and object#clone. Both doing shallow copy. Also, when I do this a = Hash.new puts(a.id) Ruby whines no such method existed. The docs mentioned object#id, and all are descendant of object class. What’s wrong? How can I verify (other than a handful of puts) if indeed two objects do not share the same data, but each has own copy? TIA ---
**Author:** ![rickyr](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ed655f/32.png) [@rickyr](https://www.ruby-forum.com/u/rickyr)\ **Post date:** [October 8, 2009, 6:40am UTC](https://www.ruby-forum.com/t/how-to-do-explicit-copy/176819/4 "2009-10-08T06:40:32Z")
rickyr wrote: > and object#clone. Both doing shallow copy. > > TIA Ricky, there is equal? method for just this purpose ## C:\Documents and Settings\Administrator\>ri Object#eql ------------------------------------------------------------ Object#eql? obj == other =\> true or false obj.equal?(other) =\> true or false obj.eql?(other) =\> true or false ``` Equality---At the +Object+ level, +==+ returns +true+ only if ``` _obj_ and _other_ are the same object. Typically, this method is overridden in descendent classes to provide class-specific meaning. ``` Unlike +==+, the +equal?+ method should never be overridden by subclasses: it is used to determine object identity (that is, +a.equal?(b)+ iff +a+ is the same object as +b+). The +eql?+ method returns +true+ if _obj_ and _anObject_ have the same value. Used by +Hash+ to test members for equality. For objects of class +Object+, +eql?+ is synonymous with +==+. Subclasses normally continue this tradition, but there are exceptions. +Numeric+ types, for example, perform type conversion across +==+, but not across +eql?+, so: 1 == 1.0 #=> true 1.eql? 1.0 #=> false ``` in ruby 1.8.6 under windows … irb(main):001:0\> a=“this is a string” =\> “this is a string” irb(main):002:0\> b=“this is a string” =\> “this is a string” irb(main):003:0\> c=a =\> “this is a string” irb(main):004:0\> a.eql?(b) =\> true irb(main):005:0\> a.eql?© =\> true irb(main):006:0\> a.equal?(b) =\> false irb(main):007:0\> a.equal?© =\> true irb(main):008:0\> ---
**Author:** ![rickyr](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ed655f/32.png) [@rickyr](https://www.ruby-forum.com/u/rickyr)\ **Post date:** [October 8, 2009, 9:57am UTC](https://www.ruby-forum.com/t/how-to-do-explicit-copy/176819/5 "2009-10-08T09:57:10Z")
2009/10/8 rickyr [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > On Oct 6, 10:50 pm, Patrick O. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > On Oct 6, 2009, at 6:45 PM, rickyr wrote: > > > > > y = x > > > > y = x.dup may be sufficient for you (it does a shallowcopy). > > Thanks, it worked. Now, what are the differences between object#dup > and object#clone. Both doing shallow copy. It’s in the docs: ri Object#clone Object#dup irb(main):001:0\> s = “foo”.freeze =\> “foo” irb(main):002:0\> t = s.clone =\> “foo” irb(main):003:0\> t \<\< “ha!” RuntimeError: can’t modify frozen string from (irb):3 from /opt/bin/irb19:12:in `’ irb(main):004:0\> t = s.dup =\> “foo” irb(main):005:0\> t \<\< “ho!” =\> “fooho!” irb(main):006:0\> t =\> “fooho!” Cheers robert ---
**Author:** ![rickyr](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ed655f/32.png) [@rickyr](https://www.ruby-forum.com/u/rickyr)\ **Post date:** [October 8, 2009, 12:55pm UTC](https://www.ruby-forum.com/t/how-to-do-explicit-copy/176819/6 "2009-10-08T12:55:41Z")
rickyr wrote: > Also, when I do this > > a = Hash.new > puts(a.id) > > Ruby whines no such method existed. The docs mentioned object#id, and > all are descendant of object class. irb(main):004:0\> RUBY\_VERSION =\> “1.8.6” irb(main):005:0\> a={} =\> {} irb(main):006:0\> a.id (irb):6: warning: Object#id will be deprecated; use Object#object\_id =\> 22862560 irb(main):007:0\> a.object\_id =\> 22862560 hth, Siep