From: Dark Ambient <sambient@...>
Date: 2006-08-11T23:19:51+09:00
Subject: Re: Question on setting up a class and searching on objects

James,
Thank you for the explanation and example.  Ran through you code in
irb so the next step is implementing my method for a search function.
Hopefully I will only be back to say I've figured it out.

No help for now though.

Stuart

On 8/11/06, James Edward Gray II <james@grayproductions.net> wrote:
> On Aug 11, 2006, at 7:47 AM, Dark Ambient wrote:
>
> > I'm working from Ruby for Rails book but want to try and just
> > replicate some of the examples in Ruby alone.
> > One method in particular is called whole_name and would give the user
> > the ability to search a list by first_name, middle_name, or last_name.
>
> If you want to make a method to search the the individual composers,
> you will need to get them into some data structure (like an Array)
> where you can scan through them.
>
> > class Composer
> >
> > def listcomp (first_name, middle_name, last_name)
> > f = first_name
> > m = middle_name
> > l = last_name
> > end
>
> What are you intending this method to do?  Currently, it doesn't do
> anything meaningful:
>
> 1.  first_name, middle_name, and last_name are accepted as arguments
> 2.  Each of those is assigned to another local variable
> 3.  All six local variables are discarded as the method exits
>
> > def whole_name
> >    first_name + " " +
> >    (if middle_name then middle_name + " " else "" end) +
> >    last_name
> > end
> > end
>
> This method doesn't work because it uses local variables that don't
> exist in this method.  I believe this is your hang-up.
>
> Inside a class, you keep data around by putting it into instance
> variables (those start with an @ symbol).  All methods of the class
> can access the instance variables for the current object.
>
> See if this helps explain things:
>
>  >> class Name
>  >>   def initialize(first, last, middle = nil)
>  >>     # assign these local variables to instance variables...
> ?>     @first = first
>  >>     @last = last
>  >>     @middle = middle
>  >>   end
>  >>
> ?>   # create methods to read those instance variables...
> ?>   attr_reader :first, :last, :middle
>  >>
> ?>   def full
>  >>     [@first, @middle, @last].join(" ").squeeze(" ")
>  >>   end
>  >> end
> => nil
>  >> james = Name.new("James", "Gray", "Edward")
> => #<Name:0x31a5e0 @last="Gray", @first="James", @middle="Edward">
>  >> james.last
> => "Gray"
>  >> james.full
> => "James Edward Gray"
>  >> dana = Name.new("Dana", "Gray")
> => #<Name:0x314c44 @last="Gray", @first="Dana", @middle=nil>
>  >> dana.middle
> => nil
>  >> dana.full
> => "Dana Gray"
>