From: Ron Fox <fox@...>
Date: 2007-12-18T21:30:01+09:00
Subject: Re: Newbie Question: What is a class for?

One way to think of a class (a restricted definition to get you started) 
is as a data type and operations on that data type.  Objects are 
variables of that data type.

For example, consider a checking account.  That has data
(a balance), and operations: deposit, withdraw, write_check,
balance etc.

You may have several bank accounts in a bank

class BankAccount
   def initialize who account_number initial_balance
     @name           = who
     @account_number = account_number
     @balance        = initial_balance
   end

   def deposit amount
      @balance += amount
   end

   def withdraw amount
     if amount <= @balance
        @balance -= amount
     else
        raise overdraft
     end
   end
   #  and so on.
end

The class defines the data that makes up a checking account:
@name            - Name of the person who owns the account.
@account_number  - Account number of the account.
@balance         - Money currently in the account.

initialize creates a new account (called when you do a BankAccount.new).
deposit    deposits funds in the account
withdraw   withdraws funds from the account.

Each object of type BankAccount has its own private copies of @name, 
@account_number and @balance so:


rons_account = BankAccount.new("Ron, 12345, 100)
daves_account= BankAccount.new("Dave, 678, 150)

Create two objects of type bank account with very different values of 
@name, @account_number and @balance.

rons_account.withdraw 10

Affects ron's copy of @balance but not dave's.

and so on.



Matthias Borgeson wrote:
> Hello all-
> 
> I am a newbie to Ruby and have just recently gotten the hang of using 
> methods to hop in and out of the main body of my programs and am moving 
> to my next concept.
> 
> I am now trying to grasp what a class isand what is is for. I understand 
> that there a bunch of different classes, but how does that help me?
> 
> While I think of methods as little tools I can create to do things 
> whenever I want in the main program, I have no idea how a class used? I 
> have the Pickaxe and Chris Pine's book, but whle describing classes, 
> neither text really helps me understand what a class is and how it 
> functions in a ruby program.
> 
> I looked through my C++ book to understand methods and how they are 
> anologous to functions, but now I am just confused on the concept.
> 
> Any help or a point in the right direction would be appreciated
> 
> Thanks in advance
> 
> mfb
> 
> 
>