Extensions to nil which allow for more helpful error messages for people who are new to Rails.

Ruby raises NoMethodError if you invoke a method on an object that does not respond to it:

$ ruby -e nil.destroy
-e:1: undefined method `destroy' for nil:NilClass (NoMethodError)

With these extensions, if the method belongs to the public interface of the classes in NilClass::WHINERS the error message suggests which could be the actual intended class:

$ rails runner nil.destroy
...
You might have expected an instance of ActiveRecord::Base.
...

NilClass#id exists in Ruby 1.8 (though it is deprecated). Since id is a fundamental method of Active Record models NilClass#id is redefined as well to raise a RuntimeError and warn the user. She probably wanted a model database identifier and the 4 returned by the original method could result in obscure bugs.

The flag config.whiny_nils determines whether this feature is enabled. By default it is on in development and test modes, and it is off in production mode.

Methods
Constants
AS_JSON = ActiveSupport::JSON::Variable.new('null').freeze
METHOD_CLASS_MAP = Hash.new
Public Class methods
add_whiner(klass)

[ show source ]

  # File activesupport/lib/active_support/whiny_nil.rb, line 30
def self.add_whiner(klass)
  methods = klass.public_instance_methods - public_instance_methods
  class_name = klass.name
  methods.each { |method| METHOD_CLASS_MAP[method.to_sym] = class_name }
end
Public Instance methods
as_json(options = nil)

[ show source ]

  # File activesupport/lib/active_support/json/encoding.rb, line 168
def as_json(options = nil) AS_JSON end
id()

Raises a RuntimeError when you attempt to call id on nil.

[ show source ]

  # File activesupport/lib/active_support/whiny_nil.rb, line 39
def id
  raise RuntimeError, "Called id for nil, which would mistakenly be #{object_id} -- if you really wanted the id of nil, use object_id", caller
end
to_param()

[ show source ]

  # File activesupport/lib/active_support/core_ext/object/to_param.rb, line 11
def to_param
  self
end