In a Rails controller (in development mode), I somehow got an object that had an invalid or orphaned reference to its class. I'm guessing the class was reloaded at some point by Rails and the Foo constant was changed, but it's weird because I never changed app/models/foo.rb. After I restarted the Rails server the problem was gone. Rails 3.2.13

pry_session.rb

@foo # => #<Foo @id=1>
Foo.get(1) # => #<Foo @id=1>
Foo.get(1) == @foo # => false
@foo.as_json == Foo.get(1).as_json # => true

Foo.get(1) === @foo # => false
@foo.class # => Foo
Foo.get(1).class # => Foo
@foo.class == Foo.get(1).class # => false
@foo.class == Foo # => false

@foo.class.object_id # => 25485
Foo.class.object_id # => 144357
Foo.get(1).class.object_id # => 144357

@foo.class.to_s.constantize == Foo # => true
@foo.class.to_s.constantize.object_id # => 144357

@foo.class == @foo.class.to_s.constantize # => false