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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 "Called id for nil, which would mistakenly be 4 -- if you really wanted the id of nil, use object_id"
end
private
def method_missing(method, *args, &block)
if @@method_class_map.include?(method)
raise_nil_warning_for @@method_class_map[method]
else
super
end
end
def raise_nil_warning_for(klass)
raise NoMethodError, NIL_WARNING_MESSAGE % klass
end
NIL_WARNING_MESSAGE = <<-end_message unless const_defined?(:NIL_WARNING_MESSAGE)
WARNING: You have a nil object when you probably didn't expect it! Odds are you
want an instance of %s instead.
Look in the callstack to see where you're working with an object that could be nil.
Investigate your methods and make sure the object is what you expect!
end_message
end
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