Check if a constant is already defined

Question

This is a simple one, I hope. How do I check, in the following example, if a constant is already defined?

#this works
var = var||1
puts var
var = var||2
put         


        

Answer 1

CONST = 2 unless defined? CONST

See here for more about awesome defined? operator.

^{P.S. And in the future I guess you'll want var ||= 1 instead of var = var||1.}

Answer 2

CONST ||= :default_value

the above works for me on ruby 1.9.3 but fails on 1.8... well 1.8 is ancient now.

Answer 3

const_defined? API

pry> User.const_defined?("PER_PAGE")
=> true
pry> User.const_defined?("PER_PAGE123")
=> false