From: Josh Cheek <josh.cheek@...>
Date: 2012-01-29T14:22:31+09:00
Subject: Re: Class variables

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On Sat, Jan 28, 2012 at 8:11 PM, josh j. <jinjosh97@gmail.com> wrote:

> Hey guys,
>
> I'm a newbie to programming and Ruby. I'm just learning about Classes
> and wondering about instance variables inside classes.
>
> I'm in the process of making a trading card game and I have a class
> called FieldController. Now each player has at least two fields so I
> have a total of 4 different instances? of this class.
> For example:
> class FieldController
>  @@space1 = []
>  @@space2 = []
>  @@space3 = []
>  @@space4 = []
>  @@space5 = []
>  def addcard(para)
>    ...
>  end
>  def removecard
>  def list
>  etc
> end
>
> Problem: Having them as class variables doesn't work when there is
> multiple FieldControllers... Instance variables don't seem to work
> because I can't access them from within the methods such as addcard.
> Normal variables are the same.
> Questions:
> 1. How do I create variables that are specific to that particular
> instance of FieldController and can be accessed inside the methods.
>

Use instance variables, not class variables.

class FieldController
  def initialize
    @space1 = []
    @space2 = []
    @space3 = []
    @space4 = []
    @space5 = []
  end
  def addcard(para)
  end
end


Now, your numbering of variables is unusual. It might be better to have a
variable, @spaces which contains a five element array.


> 2. How can I access the variables from within an object without making a
> method as an interface, such as:
> $field1 = FieldController.new
> puts $field1.space1
>
>
Variables are not directly exposed, there must always be a method that sets
/ gets the value. Your example, however, is how things currently work, so
maybe I don't understand? (as an aside, when you create a variable with a
$dollar_sign, it becomes globally visible, so make sure this is _really_
what you want -- if it is, it likely shouldn't be).

class FieldController
  # define the getter
  def space1
    @space1
  end

  # define the setter
  def space1=(new_space)
    @space1 = new_space
  end

  def initialize
    # invoke the setter
    self.space1 = 'space one'
  end
end

# `field1` is a local variable, `$field1` would be global
field1 = FieldController.new
puts field1.space1
# >> space one

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