Ruby on Rails - Is params a method or a hash?

Question

So, I am trying out the Getting Started section of the Ruby on Rails guides here.

I did not understand a line in this tutorial. Quoting it:

The params method is the object which represents the parameters (or fields) coming in from the form.

I do have some previous experience in rails, and I always assumed params is a hash. But here they call it a method which is an object.

Is params a method or a hash? Also, in ruby, are methods also objects?

Answer 1

• params is a method that returns an ActionController::Parameters object. Think of it something like this:

  def params
    ActionController::Parameters.new(...)
  end
  

  Example (somewhere in your controller or view):

  puts params
  #=> <ActionController::Parameters ...>
  puts params.is_a? Object
  #=> true
  

• A method in Ruby always return a value (note: nil is also a value) unless that method is not defined. Keep in mind though that params is already defined by Rails even if you do not see it in your code)

• Every "returned value" of a method in Ruby is an object. Even nil value is a NilClass object. Integers, Strings, Arrays, and Hashes are also objects. Why? Because eveeeeery thing inherits/starts of from the Object class.

• If < Rails 5.1:

  • ActionController::Parameters inherits from Hash class, which means that you can use all Hash methods (see Hash methods here).

    Example:

    params.sort ...
    params.each ...
    params.has_key?(:controller)
    

• But now at >= Rails 5.1:

  • ActionController::Parameters NO LONGER inherits from Hash class, so you would think that you can no longer use methods such as the above code like .sort, or .has_key?, but you still can! because ActionController::Parameters defines its own custom methods that "look like" methods from a Hash.
    • NOTE: Not all Hash methods are redefined in ActionController::Parameters. Feel free to compare the methods HERE and HERE, in particular sort method which is Hash method was not redefined in ActionController::Parameters, so you can't do params.sort anymore in Rails >= 5.1.

Answer 2

1. The description is a little bit truncated. To be precise, it should be read as:

   The return value of the params method is [an] object ...

   A method is not an object, but when you execute a method, it always returns an object. In this case, params is a method, not an object, but has a return value, which is an object.

2. In older versions of Rails, the return value of params used to be a hash, but now, it isn't a hash.