Ruby: how to check if variable exists within a hash definition

Question

I'm new to Ruby. Is there a way to do the following?

hash = {
  :key1  => defined? value1 ? value1 : nil, 
  :key2  => defined? value2 ? value2 : nil
}

puts hash[:key1] # outputs: ["expression"]

The above code stores the expression, instead of the value (if it is defined) or nil (if it is not defined).

Could you try to explain a little bit more? I've read your question three times and still don't understand what your problem is. — Benoit Garret, Oct 26 '11 at 14:00

score 2 · Answer 1 · answered Oct 26 '11 at 14:16

2

d11wtg answer will do. Also, by adding parentheses, the values are stored as expected:

hash = {
  :key1  => (defined? value1) ? value1 : nil, 
  :key2  => (defined? value2) ? value2 : nil
}

answered Oct 26 '11 at 14:16

Panagiotis Panagi

score 1 · Accepted Answer · answered Oct 26 '11 at 14:07

1

You're looking for lambda, or Proc.

hash = {
  :key1 => lambda { defined?(value1) ? value1 : nil },
  :key2 => lambda { defined?(value2) ? value1 : nil }
}

hash[:key1].call

answered Oct 26 '11 at 14:07

d11wtq

Thanks for this. Just found that by adding parenthesis does what I was looking for .... `hash = {:key1 => (defined? value1) ? value1 : nil}` – Panagiotis Panagi Oct 26 '11 at 14:12

score 0 · Answer 3 · answered Oct 26 '11 at 14:06

0

What exactly do you want to do?

hash[:key].nil?

will return true or false, depending if the key exists. Not sure if that's what you are looking for.

answered Oct 26 '11 at 14:06

Allan Nørgaard

3 Answers3