Check if a constant is already defined

RubyConstants

Ruby Problem Overview

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
puts var

#this doesn't
CONST = CONST||1
puts CONST
CONST = CONST||2
puts CONST

=> 1
   1
   uninitialized constant CONST (NameError)

Ruby Solutions

Solution 1 - Ruby

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.

Solution 2 - Ruby

const_defined? API

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

Solution 3 - Ruby

CONST ||= :default_value

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

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Content TypeOriginal AuthorOriginal Content on Stackoverflow
QuestionpeterView Question on Stackoverflow
Solution 1 - RubyjibielView Answer on Stackoverflow
Solution 2 - RubyrusllonrailsView Answer on Stackoverflow
Solution 3 - RubyakostadinovView Answer on Stackoverflow