Class variables

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.
  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

The answer is going to be super obvious but I’m a newb so…

Thanks for your time
Joshua

On Sat, Jan 28, 2012 at 8:11 PM, josh j. [email protected] wrote:

@@space1 = []
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.

  1. 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

Thanks for your response so quickly!

  1. I was using instance variables but used class variables in the
    example to demonstrate the problem about multiple instances of
    FieldController.
  2. I forgot to put the initialize method around the variables in the
    example
  3. To make it easy to read I re wrote it as simply as possible(cutting
    most methods from it). Each Space1,2 etc has 3 values, all the variables
    are then inside another variable called @allspaces (by mistake omitted
    this)
  4. I’m not really sure if I need to use a global variable but I’ll try
    not using it.
  5. I’m not even sure what wasn’t working because I was doing pretty much
    everything you said but I re wrote it and now it works. Before when I
    tried to go “field1.addcard(parameters)” it would do this (simplified)
    @allspaces.each{|space|
    if space[0] == 0
    space[0] = 1
    end
    }
    but after this I would try outputting @allspaces and no vales were
    changed, now it works!

Regards Joshua

On Sun, Jan 29, 2012 at 1:33 PM, jake kaiden [email protected]
wrote:

Variables are not directly exposed, there must always be a method that
sets / gets the values

you could use attr_accessor -

attr_accessor doesn’t get around this, it writes methods that access the
instance variables. In fact, it writes the same methods that I did (I
wrote
them out intentionally to make the relationship between the variable and
the method more apparent).

Variables are not directly exposed, there must always be a method that
sets / gets the values

you could use attr_accessor -

class FieldController
attr_accessor :space1, space2

def initialize
@space1 = []
@space2 = []
end

end

then…

fc = FieldController.new
p fc.space1
fc.space1 << “hi there”
p fc.space1

hth-

  • j

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Saludos,

El 29/01/2012, a las 19:37, “jake kaiden” [email protected]
escribió:

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