Using the question mark for string equations.

Roy van der Meij di 22 jun 10

In rails we have the method Rails.env.production? which simply checks if Rails.env equals “production”

I kinda liked that and I was curious how they did that.
It appears that DHH himself made a class StringInquirer which had a nifty method_missing method.

Let’s check it out! (you can find this file in gems/active_support#{version}/lib/active_support/string_inquirer.rb)

  module ActiveSupport
    class StringInquirer < String
      def method_missing(method_name, *arguments)
        if method_name.to_s[-1,1] == "?"
          self == method_name.to_s[0..-2]
        else
          super
        end
      end
    end
  end

With this knowledge we can do something like this.

  fancyness = ActiveSupport::StringInquirer.new("fancy")
  fancyness.fancy?
   => true
  fancyness.lame?
   => false

So what do we do when we want to make this core functionality for any stringg?
Simple! Monkey patch the class String!

  class String
    def method_missing(method_name, *arguments)
      if method_name.to_s[-1,1] == "?"
        self == method_name.to_s[0..-2]
      else
        super
      end
    end
  end

  "fancy".fancy?
   => true
  a = "awesome"
  a.awesome?
   => true
  a.stupid?
   => false

I personally like it more to have core extensions in separate modules instead of hacking the String class directly. So here is the cleaned up version.

module CoreExtensions
  module StringExtensions
    def method_missing(method_name, *arguments)
      if method_name.to_s[-1,1] == "?"
        self == method_name.to_s[0..-2]
      else
        super
      end
    end
  end
end

String.send :include, CoreExtensions::StringExtensions

"fancy".fancy?
 => true

So… is it fancy?

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