Ruby’s Hash Vs ActiveSupport’s HashWithIndifferentAccess

The Hash class in Ruby’s core library retrieves values by doing a standard == comparison on the keys. This means that a value stored for a Symbol key (e.g. :some_value) cannot be retrieved using the equivalent String (e.g. ‘some_value’). 

On the other hand, class HashWithIndifferentAccess is inherited from ruby "Hash" & a special behavior is added in it. HashWithIndifferentAccess treats Symbol keys and String keys as equivalent so that the following would work:

h = HashWithIndifferentAccess.new
h[:my_value] = 'foo'
h['my_value'] #=> will return "foo"

How can you achieve the same effect as multiple inheritance using Ruby? What is mixin?

Ruby offers a very neat alternative concept called mixin. Modules can be imported inside other class using mixin. They are then mixed-in with the class in which they are imported.

Here’s an example:

module Debug
  def whoAmI?
    "I am #{self.to_s}"
  end
end

class Photo
 include Debug
end

ph = Photo.new

"I am : #<Photo:0x007f8ea218b270>"

As you can see above the class Debug and it’s method “whoamI?” were mixed-in (added) with the class Photo.

That’s why you can now create an instance of the Photo class and call the whoAmI? method.

ph.whoAmI?
 => "I am : #<Phonograph:0x007f8ea218b270>"