```ruby 
[1] pry(main)> User.first.albums.size
  User Load (0.6ms)  SELECT `users`.* FROM `users` ORDER BY `users`.`id` ASC LIMIT 1
   (0.3ms)  SELECT COUNT(*) FROM `albums` WHERE `albums`.`user_id` = 1
=> 2
[2] pry(main)> User.first.albums.count
  User Load (0.3ms)  SELECT `users`.* FROM `users` ORDER BY `users`.`id` ASC LIMIT 1
   (0.2ms)  SELECT COUNT(*) FROM `albums` WHERE `albums`.`user_id` = 1
=> 2
[3] pry(main)> User.first.albums.length
  User Load (0.4ms)  SELECT `users`.* FROM `users` ORDER BY `users`.`id` ASC LIMIT 1
  Album Load (0.2ms)  SELECT `albums`.* FROM `albums` WHERE `albums`.`user_id` = 1
=> 2
[4] pry(main)> User.size
NoMethodError: undefined method `size' for #<Class:0x007fba0759da80>
from /Users/natsuki/workspace/sepia/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/dynamic_matchers.rb:22:in `method_missing'
[5] pry(main)> User.count
   (0.4ms)  SELECT COUNT(*) FROM `users`
=> 4
[6] pry(main)> User.length
NoMethodError: undefined method `length' for #<Class:0x007fba0759da80>
from /Users/natsuki/workspace/sepia/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/dynamic_matchers.rb:22:in `method_missing'
[7] pry(main)> 123.size
=> 8
[8] pry(main)> 123.count
NoMethodError: undefined method `count' for 123:Fixnum
from (pry):8:in `__pry__'
[9] pry(main)> 123.length
NoMethodError: undefined method `length' for 123:Fixnum
from (pry):9:in `__pry__'
[10] pry(main)> 123.to_s.length
=> 3
[11] pry(main)> 123.to_s.count
ArgumentError: wrong number of arguments (0 for 1+)
from (pry):11:in `count'
[12] pry(main)> 123.to_s.size
=> 3
```

こんな感じ？