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# Extensions to nil which allow for more helpful error messages for
# people who are new to rails.
#
# The aim is to ensure that when users pass nil to methods where that isn't
# appropriate, instead of NoMethodError and the name of some method used
# by the framework users will see a message explaining what type of object
# was expected.
class NilClass
WHINERS = [ ::ActiveRecord::Base, ::Array ]
@@method_class_map = Hash.new
WHINERS.each do |klass|
methods = klass.public_instance_methods - public_instance_methods
methods.each do |method|
@@method_class_map[method.to_sym] = klass
end
end
def id
raise RuntimeError, "Called id for nil, which would mistakenly be 4 -- if you really wanted the id of nil, use object_id", caller
end
private
def method_missing(method, *args, &block)
raise_nil_warning_for @@method_class_map[method], method, caller
end
def raise_nil_warning_for(klass = nil, selector = nil, with_caller = nil)
message = "You have a nil object when you didn't expect it!"
message << "\nYou might have expected an instance of #{klass}." if klass
message << "\nThe error occurred while evaluating nil.#{selector}" if selector
raise NoMethodError, message, with_caller || caller
end
end
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