From: tamouse mailing lists <tamouse.lists@...>
Date: 2013-05-01T02:13:50+09:00
Subject: Re: BEGINNER -CLASS QUERY

On Tue, Apr 30, 2013 at 6:27 AM, shaik farooq <lists@ruby-forum.com> wrote:
> tamouse mailing lists wrote in post #1107282:
>> On Apr 29, 2013 12:17 PM, "shaik farooq" <lists@ruby-forum.com> wrote:
>>>
>>> So in ruby we dont declare the instance variables in class for instances
>>> of class.
>>
>> When you say "declare", what is it you actually mean? "Declare" to me
>> means
>> "declare what type a variable is" and that makes no sense in Ruby.
>>
>> You can define instance (preceeded by @) and class (preceede by @@)
>> variables in a class, but that is not "declaring" them.
>
>
> Here u go "GEEK"

What does this mean?





> And moreover coming to u r language defition
> yeah my doubt is related to "Defining" not "declaration"

>
>
> Generally in java
>
> class e
> {
> int a;
> int add(){}
> }
> //main method
> e f=new e();
>
> now the instance of "e" ie "f"
> will contain the copy of instance variables
>
> but in RUBY
>
> class e
>
> def method
>
>
> end
>
> end
>
>
> f=e.new()
>
>
> now the instance of "e" ie "f" will contain the instance variables
>
>
> which are not defined in class
> i just want to have clarity on it

In the RUby class you showed, there are no instance variables present.

A Ruby class with an instance variable:

class MyClass

  def initialize(value=nil)
    @this_instance_value = value # this creates an *instance variable*
called "@this_instance_value" - note the @
  end

  def to_s
    @this_instance_value.to_s # this returns the value of "@this_instance_value"
  end

end

f = MyClass.new "hello, world"
puts f
# => hello, world

g = MyClass.new "goodbye, cruel world"
puts g
# => goodbye, cruel world


A common way of working with instance variables is to use attr methods:

class MyOtherClass

  attr_accessor :inst_var

  def initialize(value=nil)
    self.inst_var = value
  end

end

f = MyOtherClass.new # note, no value passed here; legal because of
default to nil above
f.inst_var = 1
puts f.inst_var
# => 1
f.inst_var = "HI, MOM!"
puts f.inst_var
# => HI, MOM!


>
> And moreover coming to u r language defition
> yeah my doubt is related to "Defining" not "declaration"

Ruby is not Java; Java is not Ruby. Both are object-oriented, and have
some conceptual commonalities, but are really quite different.

I'm not really aware of any good resources for coming to Ruby from
Java; I did find this slide presentation:
http://www.slideshare.net/mbowler/ruby-for-java-programmers, but
slides with no talk are pretty useless.