From: John Joyce <dangerwillrobinsondanger@...>
Date: 2007-06-16T22:03:40+09:00
Subject: Re: test to see if a variable exists


On Jun 15, 2007, at 4:58 PM, Morton Goldberg wrote:

> 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
>
>
>
An array could indeed work. Think about the structure of a SSN:  
377-23-4736  (not a real one)
That looks like a multi-dimensional array to me.
each part is limited: 3 digits, 2 digits, 4 digits.
Much like IPv4 this can produce a lot of distinct numbers.
These smaller parts are easier to process, possibly less overhead.