2005-06-20 07:15:46 -04:00
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# Extensions to nil which allow for more helpful error messages for
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# people who are new to rails.
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#
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# The aim is to ensure that when users pass nil to methods where that isn't
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# appropriate, instead of NoMethodError and the name of some method used
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# by the framework users will see a message explaining what type of object
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# was expected.
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class NilClass
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2005-06-25 07:15:38 -04:00
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WHINERS = [ ::ActiveRecord::Base, ::Array ]
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2005-06-20 07:15:46 -04:00
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@@method_class_map = Hash.new
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WHINERS.each do |klass|
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methods = klass.public_instance_methods - public_instance_methods
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methods.each do |method|
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@@method_class_map[method.to_sym] = klass
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end
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end
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2005-06-21 12:36:40 -04:00
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def id
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2005-07-04 05:54:30 -04:00
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raise RuntimeError, "Called id for nil, which would mistakenly be 4 -- if you really wanted the id of nil, use object_id", caller
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2005-06-21 12:36:40 -04:00
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end
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2005-06-20 07:15:46 -04:00
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private
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def method_missing(method, *args, &block)
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if @@method_class_map.include?(method)
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2005-07-04 05:54:30 -04:00
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raise_nil_warning_for @@method_class_map[method], caller
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2005-06-20 07:15:46 -04:00
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else
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super
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end
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end
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2005-07-04 05:54:30 -04:00
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def raise_nil_warning_for(klass, with_caller = nil)
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raise NoMethodError, NIL_WARNING_MESSAGE % klass, with_caller || caller
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2005-06-20 07:15:46 -04:00
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end
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NIL_WARNING_MESSAGE = <<-end_message unless const_defined?(:NIL_WARNING_MESSAGE)
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WARNING: You have a nil object when you probably didn't expect it! Odds are you
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want an instance of %s instead.
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Look in the callstack to see where you're working with an object that could be nil.
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Investigate your methods and make sure the object is what you expect!
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end_message
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end
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