alternatives to Hash#index that works without warning in both Ruby 1.8 and 1.9

Question

I've got some ruby code that I'm converting to Ruby 1.9. One warning I get is Hash#index is deprecated; use Hash#key

But Hash#key is not defined in Ruby 1.8, so I can't use that directly. Does anybody have a good alternative?

I've got a couple of options (which I'll post as answers so you can vote), but I'm hoping for better.

Answer 1

One possibility is:

(hash.respond_to?(:key) ? hash.key(t) : hash.index(t))

But that's gross and adds overhead.

Answer 2

Another choice is to monkeypatch:

class Hash
  alias_method(:key, :index) unless method_defined?(:key)
end

Answer 3

It's rather ugly, but works too:

h = { :a => 1 }
[:key,:index].find{|method| break h.send(method, 1) if h.respond_to?(method) }

Answer 4

require 'backports'
{:hello => :world}.key(:world)  # ==> :hello on all ruby versions

My backports gem defines all of Ruby 1.8.7 and many Ruby 1.9 methods. This makes it much easier to have code that works on all of these platforms.