From: Filipe <filipedlarcanjo@...>
Date: 2007-11-24T08:24:59+09:00
Subject: Re: Class variable as parameter

On 23 nov, 20:00, Morton Goldberg <m_goldb...@ameritech.net> wrote:
> On Nov 23, 2007, at 4:20 PM, Filipe wrote:
>
>
>
> > I have the following situation:
>
> > class MyClass
> >    def setVar(var,varValue)
> >       var=varValue
> >    end
>
> >    def initialize
> >        @myVar=0
> >        setVar(@myVar,1)
> >        puts(@myVar.to_s)
> >    end
> > end
>
> > test = MyClass.new
>
> > Unfortunately, this piece of code is returning 0 instead of the 1 I
> > would expect. Is there anything I could do?
>
> Your call to setVar can not change the value of an variable. Only
> values of variables are passed in Ruby, not the variables themselves.
>
>     def setVar(var,varValue)
>        var=varValue # <-- this is the same as: return varValue
>     end
>
>     def initialize
>         @myVar=0
>         setVar(@myVar,1) # <-- at this point this is the same as:
> setVar(0,1)
>         puts(@myVar.to_s)
>     end
>
> Ruby has a built-in method, Object#instance_variable_set that you can
> use for situations where you need to assign by name, so you don't
> need to define it for any derived class. Also, Ruby can define
> accessor methods for you:
>
> class MyClass
>     attr_accessor :myVar
>     def initialize
>         @myVar=0
>         self.myVar = 1
>         puts myVar # <-- to_s not needed; puts applies to_s to objects
>     end
> end
> test = MyClass.new
>
> This will output 1 and may be what you are looking for.
>
> Regards, Morton

The key point is that the setVar method is supposed to do a couple
more things than just set the value of the variable. I removed them
from the example just for the sake of simplicity. Something like:

class MyClass
   def setVar(var,varValue)
      var=varValue
      #do something else...
   end

   def initialize
       @myVar1=0
       @myVar2=0
       @myVar3=0

       setVar(@myVar,1)
       setVar(@myVar,2)
       setVar(@myVar,3)

   end
end

test = MyClass.new

Beeing able to "send" the variable to setVar and have its value
changed would save me many lines of code...