From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2010-10-11T18:56:45+09:00
Subject: Re: Some newbie questions - bare with me ;)

On Mon, Oct 11, 2010 at 11:35 AM, egervari <ken.egervari@gmail.com> wrote:
> Question 1
> I was curious what ":" before a identifier was exactly. It seems that
> it's often used as a map key... but what is it exactly?
>
> Printing :bob to the screen results in "bob"... but testing for
> equality between :bob and "bob" results in a falsehood.
>
> I figure this has to be some literal notation for something, but what?

It's a Symbol.

http://ruby-doc.org/core/classes/Symbol.html

A Symbol is an object of which there only exists one. Every time you
use the literal :bob, it's the same object. They are usually used as
Hash keys, as flags, and so on.

> Question 2
> In RSpec, it uses == for equality. I overrode the eql?() method in
> object, but == doesn't use it. I am used to languages providing an
> equals() method that you can override. So if you want 1:1 equals, you
> must use eql? and == is just comparing the object id's? So does that
> mean that the literal 1 uses the same object no matter where that
> literal is used?
>
> It just seems a little weird to me that if everything is an object...
> then my assumption would be that == would compare the actual state and
> not the object references like it does in Java. Can you clear this up?
> Thanks!

Check this:
http://ruby-doc.org/core/classes/Object.html

methods ==, eql? and equals?

Also this:

http://blog.rubybestpractices.com/posts/rklemme/018-Complete_Class.html

There's a very good explanation about the equivalence concepts and
best practices in Ruby.

> Question 3
> Ruby seems to @ in front of an identifier to denote that it's an
> instance variable. I'm curious, what is the reason for this? And if
> these variables are in fact private to the object, is there some kind
> of short-hand to create getter/setters?, or do you have to define
> these 2 def's yourself? I guess if that's the case, it's no worse than
> in Java, but Scala provides several ways to get around this. I'm
> curious if such shorthands exist.

attr_accessor :a      # creates methods a= and a
attr_reader              # creates method a
attr_writer               # creates method a=

Jesus.