Question

When I run ri Hash, the stringify_keys method shows up as an instance method in some of the listings where, each listing appears to be associated with a different gem or gem version.

But when I try calling it from the irb shell, it fails:

irb(main):035:0> h
=> {:this=>"this value", :that=>"that value"}
irb(main):031:0> h.instance_of? Hash
=> true
irb(main):032:0> h.stringify_keys
NoMethodError: undefined method `stringify_keys' for {:this=>"this value", :that=>"that value"}:Hash
        from (irb):32
        from /usr/local/bin/irb:12:in `<main>'

Also, when I run h.methods.sort in IRB, stringify_keys isn’t listed as a method.

Can someone explain this discrepancy? Is it a matter of my environment being outdated or just something I don’t understand about the Ruby documentation?

Answer 1

Rails (via ActiveSupport) monkey patches the stringify_keys method into Hash so you won’t have it in a plain irb session. You can load the core extensions by saying:

require 'active_support/core_ext'

See the Active Support Core Extensions Guide for details on loading individual monkey patches.