From: Dan Drew <dan@...>
Date: 2010-04-08T23:20:19+09:00
Subject: Re: Ruby newbie - Trying to understand variables

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When you use attr_reader it declares a method on your class for you like =
this:

def isbn
    return @isbn
end

You're correct that the variable in your constructor is local to that =
scope. When you call book.isbn you are actually calling the method above =
which correctly returns the instance variable.

Similarly if you used attr_accessor or attr_writer you would get a =
setter method:

def isbn=3D(val)
    @isbn =3D val
end
dan drew > brilliantsoftware.ca > shouldn't your software be brilliant?=20


From: Sask Khan=20
Sent: Thursday, April 08, 2010 9:36 AM
Newsgroups: comp.lang.ruby
To: ruby-talk ML=20
Subject: Ruby newbie - Trying to understand variables


Hey guys,

Im new to Ruby and totally new to the concept of Object Oriented
Programming.

At the moment, am going through Pragmatic Programmer=E2=80=99s Ruby and =
even
though am finding it to awesome, I have a few questions

Below is the exercise we are going through in the chapter =
=E2=80=98Classes,
Object & Variables=E2=80=99:

classBookInStock
attr_reader :isbn, :price
Def initialize(isbn,price)
@isbn =3D isbn
@price =3D Float(price)
end
Def price=3D(new_price)
@price =3D new_price
end
#...
End
book=3DBookInStock.new("isbn1",33.80)
Puts "ISBN =3D #{book.isbn}"
puts"Price =3D #{book.price}"
book.price =3D book.price*0.75       #discount price
puts"Newprice=3D #{book.price}"

Im a bit confused about the output syntax using =E2=80=98Puts=E2=80=99. =
Now, I read and
understand that the variable =E2=80=98@isbn=E2=80=99 is not the same as =
=E2=80=98isbn=E2=80=99 variable,
same for the =E2=80=98:isbn=E2=80=98 constant, all three being different =
to eachother.
The variable with =E2=80=98@=E2=80=99 is available outside the place =
where it is defined
so why are we not using the following code:

Puts =E2=80=9CISNB =3D #{book.@isbn}=E2=80=9D

Instead of  (as per the code in the exercise above)

puts =E2=80=9Cisbn=3D #{book.isbn}=E2=80=9D

The reason I think we should be using the variable with @ is because the
one without @ is not accessible outside where it is defined, right? And
as the two variables (@isbn, isbn) are different to each other. Also,
how is the constant =E2=80=98:isbn=E2=80=99 in =
=E2=80=98attr_reader=E2=80=99 connected to the =E2=80=98isbn=E2=80=99
variable when we didn=E2=80=99t connect them?




Any help would be most appreciated.
--=20
Posted via http://www.ruby-forum.com/.


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