chained_lookup.rb

class Message
  def initialize(method_name, *args, &block)
    @method_name = method_name
    @args = args
    @block = block
  end

  def call(value)
    value.send(@method_name, *@args, &@block)
  end
end

class ChainedLookup
  def initialize(messages = [])
    @messages = messages
  end

  def to_s
    ChainedLookup.new(
      @messages + [Message.new(:to_s)]
    )
  end

  def method_missing(method_name, *args, &block)
    ChainedLookup.new(
      @messages + [
        Message.new(
          method_name,
          *args,
          &block
        )
      ]
    )
  end

  def respond_to?(method_name, include_private = false)
    true
  end

  def to_proc
    Proc.new do |object|
      @messages.reduce(object) do |value, message|
        message.call(value)
      end
    end
  end
end


this = ChainedLookup.new

p [1, 2, 3].map(&this * 5 / 2) # => [2, 5, 7]

test_hash = {
  a: ['foo', 'baz', 'bar']
}

other_hash = {
  a: ['snaz']
}

p [test_hash, other_hash].map(&this[:a][0]) # => ["foo", "snaz"]