From: Robert Klemme <shortcutter@...>
Date: 2010-08-29T18:35:12+09:00
Subject: Re: initialize instance variable problem

On 28.08.2010 18:17, Cameron Vessey wrote:
> Why does this return nil for @city?
>
> class Url
>    def initialize(city,quary,catagory,minask,maxask)
>      @city = city
>      @quary = quary
>      @cat = catagory
>      @min = minask
>      @max = maxask
>    end
>
>    puts @city
>
> end
> a = Url.new('spokane',"tires","pts","0","1000")
> a

Others have identified the basic issue (your puts statement accesses a 
member of the class and not of the instance) but I'd like to add a few 
other remarks.  First, the name Url might cause confusion because 
someone might think it is a generic URL handling class (like class URI 
for example).

What you basically should do is add attribute accessors for your 
instance variables, e.g.

class Url
   attr :city
end

Then you can do

a = Url.new ...
puts a.city

But: you can make your life much simpler by resorting to Struct:

CityUrl = Struct.new :city, :quary, :catagory, :minask, :maxask

This gives you a proper initialize, attribute accessors and a few more 
things for free.

irb(main):008:0> a = CityUrl.new('spokane',"tires","pts","0","1000")
=> #<struct CityUrl city="spokane", quary="tires", catagory="pts", 
minask="0", maxask="1000">
irb(main):009:0> a.city
=> "spokane"

Btw, from the naming and values of "minask" and "maxask" it seems these 
should be rather used with integer values.  Even if you read them as 
strings from some sort of file your application logic will become much 
easier if you convert those strings on reading into ints and then go 
from there.  Otherwise you will have to convert them all the time you 
want to use them which is inefficient, error prone (you might forget a 
location) and tedious to change if you need to at one point.  Also, you 
depend on the format of the single source which might make it difficult 
to pull the data from other sources later.  Basically it's best to 
always do something like

external representation -> import (load) converts into internal 
representation -> work with that internal representation throughout the 
application -> export (store) converts to external representation

Kind regards

	robert

-- 
remember.guy do |as, often| as.you_can - without end
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