Question

class Account
  def initialize(starting_balance = 0)
     @balance = starting_balance
  end

  def balance #instance getter method
     @balance #instance variable visible only to this object
  end

  def balance=(new_amount)
     @balance = new_amount
  end

  def deposit(amount)
     @balance+=amount
  end

  @@bank_name= "MyBank.com" # class (static) variable

  # A class method
  def self.bank_name
     @@bank_name
  end
  # or: def SavingsAccount.bank_name : @@bank_name : end

end

I want to understand the code snippets in bold. What do they do? what is the difference between a setter and initialize method.
If I had an object test=Account.new() and why is test(30) giving an error. Isn’t that suppose to call the setter method with parameter 30 and set the balance?

Answer 1

initialize is the method that is called on the newly created object when you do Account.new or Account.new(my_starting_balance). In the first case initialize would be called with the default value 0 for starting_balance and in the second with my_starting_balance.

The setter method balance= is called when you do my_account.balance = some_value where my_account is an instance of the class Account. So if you have the following code, initialize will be called on line 1 (with 0 as its argument) and balance= on line 2 (with 23) as its argument:

my_account = Account.new
my_account.balance = 23

Of course in this case I could just as well write the following and not use the setter method at all:

my_account = Account.new(23)

However that doesn’t always work because some times you might want to change the value of balance after the object has already been created.

If I had an object test=Account.new() and why is test(30) giving an error.

Because test(30) means “call the method test with the argument 30″ and there is no method called test in your code.

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Regarding the second bolded part of your code: As the comments indicate, it sets a class variable named @@bank_name and defines a class method that returns that variable’s value.