From: Jacob Fugal <lukfugl@...>
Date: 2006-02-24T01:38:19+09:00
Subject: Re: What's mean? global variables

On 2/23/06, BlueFox <blue_fox@ynmail.com> wrote:
> what is mean of(outside of the class define)
>
> def test
>    $test ||= Test.new
> end

The keyword def, as you already know, begins a method definition. When
the method definition occurs outside the scope of any class, the
current 'self' is the 'main' object. Defining a method on 'main'
through some black magic, actually creates the method as an instance
method of Object. As such, the method is available to all instances of
Object -- that is, everything. This way, the method can be called
without a receiver in any context and generally have the same behavior
(modulo instance variables, but if you're using instance variables in
top-level methods/procedures, you're asking for trouble). This makes
the method, in effect, a procedure.

$test is a global variable. Thats important in this case for scope --
$test continues to exist and retain its value between invocations of
test. The ||= idiom is one commonly found in ruby. It's similar to +=
in that it is simply short hand for "$test = $test || Test.new". $test
starts with a value of nil, and the first time test is run (unless you
manually set $test beforehand), $test is initialized to a new instance
of Test, since "(nil || anything) == anything". On subsequent runs,
$test retains its value. From this behavior, ||= can be thought of as
a "default initializer" operator.

Does that answer your questions?

Jacob Fugal