From: "Matthew, Graeme" <Graeme.Matthew@...>
Date: 2002-09-20T14:34:20+09:00
Subject: RE: Attribute Access Problems

thanks for the help, i am willing to use the attr_reader, attr_writer
options however the problem with these is that lets say you need to trigger
of some events when an attribute is set, then how would you do it through
attr_reader / writer ?

I also thought the whole aim of def projectName=(val) was to act as a getter
/ setter attribute ?

cheers


Graeme Matthew
Analyst Programmer
Mercer Investment Consulting
Level 29, 101 Collins Street, Melbourne, VIC, 3001, Australia
Tel  - 61 3 9245 5352 Fax - 61 3 9245 5330
visit http://www.merceric.com


-----Original Message-----
From: Lyle Johnson [mailto:lyle@users.sourceforge.net]
Sent: Friday, 20 September 2002 15:21
To: ruby-talk@ruby-lang.org
Subject: Re: Attribute Access Problems


Matthew, Graeme wrote:

> I'm just not getting this!

Don't Panic!

> What am I doing wrong here, this is taking way to long :-(
> 
> c:/dev/cgi-bin/Project.rb:80:in `DisplayProject': undefined method
> `projectName' for #<Project:0x25dfae0> (NameError)

OK, I know you can read, but just to clarify: this error message is 
telling you that you're trying to call an instance method named 
"projectName" for the "Project" class, but there is no instance method 
by that name.

> I'm now using instance variables
>  
> def projectName=(val)
> 		@projectName = val if val
> 		return @projectName
> end

This looks fine, but keep in mind that "projectName=()" (a "setter" 
method) and "projectName()" (a "getter" method) are *two* different 
method names...

> but it's failing here in my document:
> 
> <tr><td>Name</td><td><input type="text" name="code"
> value="#{self.projectName}"></td></tr>

Although we can't see all of the code for your "Project" class, I'm 
guessing that you didn't define a "projectName" accessor method to 
complement the "projectName=" method. A quick way to do this (since you 
also have a "@projectName" instance variable) is to use the attr_reader 
method:

     class Project
       attr_reader :projectName
     end

A more verbose (but otherwise equivalent) way to do it is to explicitly 
code-up the method:

     class Project
       def projectName
         @projectName
       end
     end

If you don't already have "Programming Ruby" (a.k.a. the "Pickaxe" book) 
I'd recommend you pick up a copy. It's also available for free online. 
The second chapter:

	http://www.rubycentral.com/book/tut_classes.html

has a section entitled "Objects and Attributes" that does a very nice 
job of explaining what's going on.

Hope this helps,

Lyle
__


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