Rails how do I check for existance of a class when not instantiated yet?

Question

I have a utility class defined with a bunch of class methods. In the Rails console, when I search for the class using Object.const_defined? it returns false. But after calling one of the class methods or creating an instance of the class, Object.const_defined? returns true. Is this because of some kind of lazy loading instantiation kind of thing? Is there another way I can check for the existence of a class which will return true, even if I haven't instantiated anything yet?

You might just try eager-loading them; if the class hasn't been loaded, it hasn't been loaded, e.g., http://stackoverflow.com/q/19839847/438992 — Dave Newton, Feb 06 '14 at 20:49

score 7 · Accepted Answer · answered Feb 06 '14 at 21:03

7

This is kind of a hack, but it works

Object.const_get(:ClassName).is_a?(Class) rescue false

Above statement will return true if the class is defined and return false otherwise

answered Feb 06 '14 at 21:03

usha

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Wouldn't `!!ClassName rescue false` be simpler? – BroiSatse Feb 06 '14 at 21:05
Yeah, that's another way – usha Feb 06 '14 at 21:11
1

How about ClassName rescue false ? ClassName is truthy if it exists =) – Abdo Feb 06 '14 at 22:31
I am wondering if there is a way to do this without exception handling? – Tigraine Dec 15 '14 at 13:42

score 6 · Answer 2 · answered Sep 07 '16 at 14:58

6

You can use safe_constantize.

  your_class = "YourClassName".safe_constantize
  if your_class && your_class.class == Class
    your_class.new(options).run
  end

answered Sep 07 '16 at 14:58

zzbazza

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Rails how do I check for existance of a class when not instantiated yet?

2 Answers2