59 lines
2.2 KiB
Ruby
59 lines
2.2 KiB
Ruby
# Extensions to +nil+ which allow for more helpful error messages for people who
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# are new to Rails.
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#
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# Ruby raises NoMethodError if you invoke a method on an object that does not
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# respond to it:
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#
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# $ ruby -e nil.destroy
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# -e:1: undefined method `destroy' for nil:NilClass (NoMethodError)
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#
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# With these extensions, if the method belongs to the public interface of the
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# classes in NilClass::WHINERS the error message suggests which could be the
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# actual intended class:
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#
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# $ script/runner nil.destroy
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# ...
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# You might have expected an instance of ActiveRecord::Base.
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# ...
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#
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# NilClass#id exists in Ruby 1.8 (though it is deprecated). Since +id+ is a fundamental
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# method of Active Record models NilClass#id is redefined as well to raise a RuntimeError
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# and warn the user. She probably wanted a model database identifier and the 4
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# returned by the original method could result in obscure bugs.
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#
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# The flag <tt>config.whiny_nils</tt> determines whether this feature is enabled.
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# By default it is on in development and test modes, and it is off in production
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# mode.
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class NilClass
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WHINERS = [::Array]
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WHINERS << ::ActiveRecord::Base if defined? ::ActiveRecord
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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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class_name = klass.name
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methods.each { |method| METHOD_CLASS_MAP[method.to_sym] = class_name }
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end
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# Raises a RuntimeError when you attempt to call +id+ on +nil+.
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def id
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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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end
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private
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def method_missing(method, *args, &block)
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raise_nil_warning_for METHOD_CLASS_MAP[method], method, caller
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end
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# Raises a NoMethodError when you attempt to call a method on +nil+.
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def raise_nil_warning_for(class_name = nil, selector = nil, with_caller = nil)
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message = "You have a nil object when you didn't expect it!"
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message << "\nYou might have expected an instance of #{class_name}." if class_name
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message << "\nThe error occurred while evaluating nil.#{selector}" if selector
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raise NoMethodError, message, with_caller || caller
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end
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end
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