mirror of
https://github.com/rails/rails.git
synced 2022-11-09 12:12:34 -05:00
58 lines
2.2 KiB
Ruby
58 lines
2.2 KiB
Ruby
# Extensions to +nil+ which allow for more helpful error messages for people who
|
|
# are new to Rails.
|
|
#
|
|
# Ruby raises NoMethodError if you invoke a method on an object that does not
|
|
# respond to it:
|
|
#
|
|
# $ ruby -e nil.destroy
|
|
# -e:1: undefined method `destroy' for nil:NilClass (NoMethodError)
|
|
#
|
|
# With these extensions, if the method belongs to the public interface of the
|
|
# classes in NilClass::WHINERS the error message suggests which could be the
|
|
# actual intended class:
|
|
#
|
|
# $ script/runner nil.destroy
|
|
# ...
|
|
# You might have expected an instance of ActiveRecord::Base.
|
|
# ...
|
|
#
|
|
# NilClass#id exists in Ruby 1.8 (though it is deprecated). Since +id+ is a fundamental
|
|
# method of Active Record models NilClass#id is redefined as well to raise a RuntimeError
|
|
# and warn the user. She probably wanted a model database identifier and the 4
|
|
# returned by the original method could result in obscure bugs.
|
|
#
|
|
# The flag <tt>config.whiny_nils</tt> determines whether this feature is enabled.
|
|
# By default it is on in development and test modes, and it is off in production
|
|
# mode.
|
|
class NilClass
|
|
WHINERS = [::Array]
|
|
WHINERS << ::ActiveRecord::Base if defined? ::ActiveRecord
|
|
|
|
METHOD_CLASS_MAP = Hash.new
|
|
|
|
WHINERS.each do |klass|
|
|
methods = klass.public_instance_methods - public_instance_methods
|
|
class_name = klass.name
|
|
methods.each { |method| METHOD_CLASS_MAP[method.to_sym] = class_name }
|
|
end
|
|
|
|
# Raises a RuntimeError when you attempt to call +id+ on +nil+.
|
|
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
|
|
|
|
# Raises a NoMethodError when you attempt to call a method on +nil+.
|
|
def raise_nil_warning_for(class_name = 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 #{class_name}." if class_name
|
|
message << "\nThe error occurred while evaluating nil.#{selector}" if selector
|
|
|
|
raise NoMethodError, message, with_caller || caller
|
|
end
|
|
end
|
|
|