Why is this module's initialize method not called when it is included in Temp class?
module Temp
def initialize
p "asdasd"
end
end
class Swap
include Temp
def initialize
p "m in class"
end
end
s = Swap.new
m in class
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3 Answers
The Swap class overrides the initialize method defined in the Temp module. When Ruby attempts to find a method it searches the inheritance hierarchy starting at the most derived class/module. In this case the search ends at the Swap class.
Overridden methods don't get called unless you explicitly call them with super. For example
class Swap
include Temp
def initialize
p "m in class"
super
end
end
will call Temp#initialize from Swap#initialize.
Comments
Because you defined initialize in both the class and module, and Ruby will look for methods in its own class before moving up to other classes/module.
To see the chain of ancestors, try this
s = Swap.new
puts s.class.ancestors
You will see the chain, and know where Ruby starts to find its function.
Comments
It only calls the constructor within scope.
If you want to invoke the modules initializer method you have to call it directly like so.
module Temp
def self.initialize
p "asdasd"
end
end
class Swap
include Temp
def initialize
p "m in class"
Temp.initialize
end
end
s = Swap.new
2 Comments
Rye Biesemeyer
In this example, since scope isn't really needed, this works. But if the Temp#initialize method needs to be called in the scope of the Swap instance, you'll run into problems.
Ed Ruder
Calling
Temp.initialize is an anti-pattern--super is the right way to call the initialize method of the super-class.