Test to see if a variable exists

Ruby
1

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)

2

On Jun 15, 2:36 pm, “Colin S.” [email protected] 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?

Arrays (and Hashes) in Ruby are sparse - they only store the values
you actually enter. However, there are some limitations on the size of
indices for arrays:

C:>irb

irb(main):001:0> ss = []
=> []

irb(main):002:0> ss[ 884_56_2103 ] = “I HAVE YOU NOW”
ArgumentError: index too big
from (irb):2:in `[]=’
from (irb):2

So, you probably want to use a Hash, which has no such limitation.
With both Arrays and Hashes, supplying a key or index which has no
stored value will return a nil object:

irb(main):003:0> ss = {}
=> {}

irb(main):004:0> ss[ 884_56_2103 ] = “I HAVE YOU NOW”
=> “I HAVE YOU NOW”

irb(main):005:0> ss[ 912_34_3552 ]
=> nil

In Ruby, nil and false are both non-truth values for the purposes of
boolean logic. Additionally (and slightly more cleanly), you can ask a
Hash directly if it has an entry for a specific key:

irb(main):006:0> if ss.has_key?( 884_56_2103 ) then
irb(main):007:1* puts “I’m done with this guy”
irb(main):008:1> else
irb(main):009:1* puts “Sweet new information!”
irb(main):010:1> end
I’m done with this guy

3

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

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.

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

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

4

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

I already have it? Does

Stolen = {}
Stolen[ss1].process rescue nil # process runs

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.

5

On Jun 16, 2007, at 9:03 AM, John J. wrote:

ss[34323843] = Stolen_identity.new

  puts "#{@ss}: I've been stolen!"

Stolen[ss1].process if Stolen[ss1] # process runs

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.

I don’t doubt that Identity objects could be indexed into some kind
of array, but I do think the hash approach is simpler and easier to
implement. I’d be happy to be convinced otherwise. How about posting
some code to prove your point?

Regards, Morton