MethodHuntingDelegator

example.rb

class Book < SomeModelThing
  attr_reader :title, :blurb
end

class Course < SomeModelThing
  attr_reader :name, :description
end

class SearchResult < MethodHuntingDelegator

  def description
    hunt_and_call :description, :blurb
  end

  def title
    hunt_and_call :title, :name
  end

end

# simulate the results of a search with mixed result types
results = [ Book.first, Course.first ].map(&SearchResult.method(:new))

results.each { |r| puts "#{r.title}: #{r.description}" }

method_hunting_delegator.rb

require "delegate"

class MethodHuntingDelegator < SimpleDelegator

  def hunt_and_call *candidates
    hunt_method(*candidates).call
  end

  private

  def hunt_method *candidates
    __getobj__.method candidates.detect(
      ->{ raise Error.new(candidates, __getobj__) },
      &__getobj__.method(:respond_to?)
    )
  end

  class Error < StandardError
    def initialize candidates, object
      super "#{candidates.inspect} not implemented by #{object.inspect}"
    end
  end

end

method_hunting_delegator_spec.rb

require "spec_helper"
require "method_hunting_delegator"

describe MethodHuntingDelegator do

  context "decorating a string" do

    let(:delegate) { "abcd" }
    let(:delegator) { MethodHuntingDelegator.new(delegate) }

    describe "#hunt_and_call" do

      it "delegates [ :not_a_method, :length, :upcase ] to String#length" do
        delegator.hunt_and_call(:not_a_method, :length, :upcase).should == 4
      end

      it "raises MethodHuntingDelegator::Error for [ :nope_A, :nope_B ]" do
        expect do
          delegator.hunt_and_call(:nope_A, :nope_B)
        end.to raise_error(MethodHuntingDelegator::Error)
      end

    end

  end

end