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rails--rails/activesupport/lib/active_support/whiny_nil.rb
wycats 39d6f9e112 Make many parts of Rails lazy. In order to facilitate this,
add lazy_load_hooks.rb, which allows us to declare code that
should be run at some later time. For instance, this allows
us to defer requiring ActiveRecord::Base at boot time purely
to apply configuration. Instead, we register a hook that should
apply configuration once ActiveRecord::Base is loaded.

With these changes, brings down total boot time of a
new app to 300ms in production and 400ms in dev.

TODO: rename base_hook
2010-03-07 06:24:30 -08:00

60 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:
#
# $ rails 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
METHOD_CLASS_MAP = Hash.new
def self.add_whiner(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
add_whiner ::Array
# 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)
if klass = METHOD_CLASS_MAP[method]
raise_nil_warning_for klass, method, caller
else
super
end
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