How to detect the end of a method chain in Ruby

Question

I have a Flickr interface that I wrote a while ago and part of it bothers me and I\'d like to make it nicer. The way it works is I use method missing to construct the url parame

Answer 1

Since I can't think of any way to detect the last method call, I'm going to suggest a different approach. It is similar to what ActiveRecord does; a proxy class that builds the options and doesn't fetch the data until you call a method that operates on the data.

class Flickr
  def initialize
    @result = FlickrResult.new
  end

  def method_missing(method, *args, &block)
    if @result.data.respond_to?(method)
      @result.run(method, args, block)
    else
      @result.append(method, args[0])
      return self
    end
  end

  class FlickrResult
    attr_reader :data

    def initialize
      @data = []
      @keys = []
      @options = {}
    end

    def append(key, options)
      @keys << key
      @options.merge!(options) if options
    end

    def run(method, args, block)
      if !@did_run
        fetch_data
      end

      @data.send(method, *args, &block)
    end

    def fetch_data
      puts "Only runs once!"
      @url = @keys.join(".") + "?" + @options.map {|k, v| "#{k}=#{v}" }.join("&")
      # use @url and fetch data..
      @data = ["foo", "bar"]

      @did_run = true
    end
  end
end

@flickr = Flickr.new
@flickr.groups(:group_id => "123").pools.thing.users(:user_id => "456")

@flickr.each {|f| p f }
# => "Only runs once!"
# => "foo"
# => "bar"
p @flickr.map {|f| f.upcase }
# => ["FOO", "BAR"]

It only fetches the data when you each or map it or whatever (any array method).