Ruby on Rails - params是方法还是哈希？

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.

Answer 3

params is a method which returns an object - instance of ActionController::Parameters .

It has methods that make it behave much like a hash, but it is a bit more complex than a hash.

Also, in Ruby, are methods also objects?

Check this thread .