Module
70 | Chapter 2: ActiveSupport and RailTies
Module
Aliasing core_ext/module/aliasing.rb
- alias_method_chain(target,feature)wraps a method in a new function, usually to
add a new feature. This mechanism was discussed in Chapter 1. The method call:
alias_method_chain :target, :feature
is equivalent to:
alias_method :target_without_feature, :target
alias_method :target, :target_with_feature
One consequence is that thetarget_withfeaturemethod must exist before thealias
method_chaincall. Punctuation (at the end of ?, !, and = methods) is properly moved to
the end of the method names. - alias_attribute(new_name,old_name)aliases an ActiveRecord attribute to a new name,
adding the getter, setter, and predicate (for example,person.name?) methods.
Delegation core_ext/module/delegation.rb
Thedelegate method provides a simple way to delegate one or more methods to an object:
class StringProxy
attr_accessor :target
delegate :to_s, :to => :target
def initialize(target)
@target = target
end
end
proxy = StringProxy.new("Hello World!")
proxy.to_s # => "Hello World!"
proxy.target = "Goodbye World"
proxy.to_s # => "Goodbye World"More detailed control over delegation can be obtained withDelegatorfrom the standard
library.
Introspection core_ext/module/inclusion.rb,core_ext/module/introspection.rb
- Module#included_in_classesiterates over all classes (usingObjectSpace), collecting the
classes and modules in which the receiver is included.
Enumerable.included_in_classes.include? Array # => true
Enumerable.included_in_classes.include? String # => true
Enumerable.included_in_classes.include? Numeric # => false - Module#parent andModule#parents inspect the module namespace hierarchy:
module A
module B
class C
end
end
end