From: Rein Henrichs <reinh@...>
Date: 2010-06-08T13:55:06+09:00
Subject: Re: Defining struct in a class

On 2010-06-07 16:16:57 -0700, William Song said:

> Rein Henrichs wrote:
>> On 2010-06-07 15:16:33 -0700, William Song said:
>> 
>>> 
>>> This will give me an error message saying the push is not defined for
>>> NilClass. How should I fix this?
>> 
>> The error you reported has nothing to do with your Card struct. Besides
>> which, your code works for me as is.
> 
> Sorry, I meant to put it into a function. I over-simplified it when
> posted here.
> 
> class Cards
>     Card = Struct.new(:suit, :number)
>     @cardsOnHand=[]
> 
>     def a()
>         @cardsOnHand.push(Card.new("S","5"))
>     end
> end
> 
> cards = Cards.new
> cards.a()
> 
> The above code will give an error.

You create an instance variable, @cardsOnHand, in the class scope. That 
means it is an instance variable of the object Cards (the class). You 
then attempt to access it in the scope of an instance method, i.e. on a 
Cards instance. They are two different objects, two different scopes 
and two different variables.

I would suggest reading the chapter Classes, Objects and Variables in 
http://ruby-doc.org/docs/ProgrammingRuby to better understand the 
concept of scope in Ruby and how it effects variables. Hint: you 
probably want to set this instance variable when you *initialize* an 
Cards object.

I would also suggest reading 
http://github.com/chneukirchen/styleguide/blob/master/RUBY-STYLE to get 
a better grasp of common Ruby style, such as two space indention, 
adding spacing before and after the = in a variable assignment, using 
camel_case for variable and method names, and removing empty () on the 
ends of methods.

-- 
Rein Henrichs
http://puppetlabs.com
http://reinh.com