From: Morton Goldberg <m_goldberg@...>
Date: 2007-06-16T06:58:11+09:00
Subject: Re: test to see if a variable exists

On Jun 15, 2007, at 4:36 PM, Colin Summers wrote:

> So I am stealing all these identities and storing everything in a big
> array of objects stolen_identity, and having the index be social
> security numbers:
>
> ss[34323843] = Stolen_identity.new
>
> But say I pick up a paycheck stub and it has 3428294. How do I know if
> I already have it? Does
>   if (exist ss[3428294]) then ... end
> work? How can I see if a variable exists?
>
> Thanks.
>
> (please include your social security with your answer)

Using a hash is the way to go here. You've already been advised to do  
that. But here is an example that may give you some additional insight.

<code>
class Identity
    def initialize(ss)
       @ss = ss
    end
    def process
       puts "#{@ss}: I've been stolen!"
    end
end

Stolen = {}

ss1 = '123-12-1234'
ss2 = '789-78-7890'
Stolen[ss1] = Identity.new(ss1)

# One way
Stolen[ss1].process if Stolen[ss1] # process runs
Stolen[ss2].process if Stolen[ss2] # process does not run

# Another way
Stolen[ss1].process rescue nil # process runs
Stolen[ss2].process rescue nil # process does not run
</code>

There are many other ways, but they all rely on same thing: that  
Stolen[ss2] returns nil and nil is treated as false in boolean  
expressions.

Regards, Morton