Ruby / Rails: clone vs. dup vs. deep_dup

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Ruby and Rails have several methods for creating a new object that looks like another: clone, dup, deep_dup. When using them you should be aware of their differences so that you can select the method you really need.

clone

dup

  • Shallow copy: references to other objects/values are copied (instead of cloning those objects/values)
  • Clones the object, but ignores "special object attributes" like frozen, tainted and modules that the object has been extended with
  • Ruby 2.6 documentation for dup Show archive.org snapshot

deep_dup

  • Provided by ActiveSupport
  • "Special object attributes" like frozen, tainted and singleton methods are ignored (like dup)
  • Behavior depends on implementation

Note that deep_dup is not a silver bullet and needs to be implemented properly by the object you call it on.

Further Reading

Judith Roth
Last edit
Henning Koch
License
Source code in this card is licensed under the MIT License.
Posted by Judith Roth to makandra dev (2020-05-05 09:48)