From: dobest03 <dobest03@...>
Date: 2005-05-16T21:55:30+09:00
Subject: Newbie: pinpoint my mistake please..

Hello.

Can anyone pinoint me where I made a mistake?

Error message is as follows:
accounts.rb(main):038:0> accounts.transferToSavings(100)
NoMethodError: undefined method `balance' for 0:Fixnum
        from accounts.rb:29:in `debit'
        from accounts.rb:29:in `transferToSavings'
        from accounts.rb:42
        from :0

But if I commented out "ths doesn't works" and remove comments
on "this works" codes, it works. Don't the code

		@checking = super(checking)
		@savings = super(savings)

create a new 'Account' class instances and stores them into
instance variable of class 'Accounts' @checking and @savings
respectively?

class Account
	def initialize(balance)
		@balance = balance
	end
	attr_reader :balance
	attr_writer :balance
end

class Accounts < Account
	attr_reader :checking, :savings
	def initialize(checking, savings)
# these doesn't works
		@checking = super(checking)
		@savings = super(savings)
# but these works
#		@checking = checking
#		@savings = savings
	end
  private
	def debit(account, amount)
		account.balance -= amount
	end
	def credit(account, amount)
		account.balance += amount
	end
  public
	def transferToSavings(amount)
		# private method can be called only in the defining class
		debit(@checking, amount)
		credit(@savings, amount)
	end
end

# this doesn't work
accounts = Accounts.new(0, 10000)
# this works
#accounts = Accounts.new(Account.new(0), Account.new(10000))
accounts.balance # balance is the instance method of class 'Account'
accounts.balance = 100
accounts.checking
accounts.savings
accounts.transferToSavings(100)
accounts.checking
accounts.savings

Thanks a lot
SYLee