Need to know how hash key are handled in ruby

Question

I am working on ruby rails project. I am using Rails 2.3.4 and ruby 1.8.7 . I have a model called User.

I have following code in initializer

$h =  {User => 'I am user' }

In the controller I have following code

$h[User]

First time when I do h[User] I get the right result. However if I refresh the page then I get nil value.

I think this is what is happening.

First time when User class is loaded then I get the right value. However when I refresh the page then this time controller returns nil value for $h[User].

Because rails unloads all the constants when page is refreshed so it seems a new User class is loaded. This User class is different from the User that was used as key in initializer.

I know using User class is a bad practice. My question is can someone explain to me when User class is used as key then internally how ruby stores the key. Does ruby use object_id of User as the key? I

Answer 1

Hash calls the hash method on any objects used as a key. And yes, your theory as to why your code isn't working is correct.

Try this in the Rails console:

User.hash # => 215678765 (or whatever)
reload! 
User.hash # => 215876673

Reloading the class changed the value returned by the hash method, meaning it is no longer the same key when used in a Hash.

Use :user or something else that will resolve to the same key every time.

Answer 2

The hash method is used on each object used as a key in a Hash.