From: Sam Kong <sam.s.kong@...>
Date: 2005-08-13T04:11:10+09:00
Subject: Instance variables and method parameters

Hello!

I have a question about using instance member variables in a method.
This is rather a general OO implementation question than specific Ruby
one.

As you know, all instance methods can access insatance member variables
freely.
Thus, instance member variables are like global variables in a class (I
mean... in an object).
So you don't have to pass those data beween methods in a class.

However, I feel more comfortable when I make those data passed as
arguments.

See the examples (very simple and stupid one):

class Tax1
	def initialize(emp_id)
		@emp_id = emp_id
	end

	def tax
#explicitly pass the argument even if get_salary can access @emp_id
		salary = get_salary(@emp_id)
		return salary * 0.1
	end

	def get_salary(emp_id)
		#do some calcuation using emp_id and data from db
		#...
		return salary
	end

	private :get_salary

end

class Tax2
	def initialize(emp_id)
		@emp_id = emp_id
	end

	def tax
		salary = get_salary #no argument
		return salary * 0.1
	end

	def get_salary
		#do some calcuation using @emp_id and data from db
		#...
		return salary
	end

	private :get_salary

end


For public methods, it's obvious that you shouldn't put arguments as
the format affects objects' clients.
But for private methods, I like to make the methods more standalone
(not depending the member variables).

Is this an acceptable habit?
Do you feel the same way as I do?

Thanks.

Sam