The send method - Ruby metaprogramming

gistfile1.rb

Consider a simple blogging app on Rails. Lets say, I have a list of articles, and I'd like to filter them by today's articles and this week's articles.

I'd like to define two methods in the model that does the actual filtering.

class Article < ActiveRecord::Base
  def self.this_week
    Article.where("created_at > ?", Date.today.beginning_of_week)
  end

  def self.today
    Article.where("created_at > ?", Date.today)
  end
end

So In my index.html.erb I have two links (in HAML, for brevity) :

    = link_to "Filter by today", filter_articles_path(:time_range => "today")
    = link_to "Filter by today", filter_articles_path(:time_range => "this_week")

Lets define a simple filter action in the articles controller : 

def ArticlesController < ApplicationController
  def filter
    Article.send(params[:time_range])
    render :index
  end
end

The send method dynamically decides which method to call. i.e it "sends" the argument as the method call.
So, in the example, if click on the "This week" link, the params[:time_range] will be "this_week" and Ruby in runtinme interprets

Article.send(params[:time_frame])
as

Article.this_week

which invokes the class level "this_week" method we earlier declared in the Article model.