class ActiveSupport::Deprecation::DeprecatedInstanceVariableProxy

def initialize(instance, method, var = "@#{method}")

:nodoc:
which emits deprecation warnings on any method call (except +inspect+).
Stand-in for @request, @attributes, @params, etc. 
def initialize(instance, method, var = "@#{method}")
  @instance, @method, @var = instance, method, var
end