solutions to the annoying "warning: already initialized constant" message

Question

Today I've stumbled upon a tricky issue with Ruby constants. In our team someone created a module, which is included into multiple models. In our (spec) test output this results into warning messages such as:

/home/ayrton/project/lib/life_cycle.rb:5: warning: already initialized constant RESET

One way to solve this is, is to declare your constants like this:

module LifeCycle

  unless (const_defined?(:RESET))
    RESET = 'reset'
  end

  #...
end

I've also read a blog post, written by Avdi Grimm, which provides an alternative solution, I was wondering what your opinions are, regarding this matter.

Do you mean it is `require`d in multiple models, or `include`d? It should be loaded only once even if `require`d multiple times — Marc-André Lafortune, Oct 31 '11 at 13:49

score 145 · Answer 1 · answered May 08 '14 at 20:55

145

I encountered this same problem today and found a simple solution.

Since the warning is from trying to reassign a constant with its same value, I just changed

module LifeCycle
  RESET = 'reset'
end

to

module LifeCycle
  RESET ||= 'reset'
end

This took care of the warning and is a lot simpler than checking if each constant is defined. Let me know if you find a better solution.

answered May 08 '14 at 20:55

Matthew Leonard

1,965
1
13
10

2

This takes care of the warning very neatly. – Valerio Schiavoni Jun 03 '15 at 16:27
4

Memoizing is a good solution if the warning is caused by your class being reloaded. If you're overriding constants from 3rd-party classes it's safer to leave the warning in place. – Thiago Figueiro Nov 20 '15 at 04:53
This works for Ruby but Rubocop is throwing an error when doing that: `An error occurred while Style/MutableConstant cop was inspecting ` – anthony Jul 20 '16 at 17:33
1

I forgot about this, but its the perfect solution when you use require_relative – chasethesunnn May 13 '19 at 03:37
Keep in mind this doesn't help if the constant is equal to `false` (or `nil`). – mckeed Jul 01 '22 at 17:23

score 25 · Answer 2 · answered Nov 08 '11 at 08:04

25

This is only a problem in applications that explicitly reload, like Rails applications.

If the verbosity offends you, you can use unless as a statement modifier instead:

module LifeCycle
  RESET = 'reset' unless const_defined?(:RESET)
end

This leaves a few weak arguments against Avdi's suggestion to only use methods:

constant lookup is faster than method lookup,
constant values are defined on load, not on (first) request,
constants visually suggest that they require no work to derive, and

If you like Avdi's suggestion enough to ignore these, go with it.

answered Nov 08 '11 at 08:04

sheldonh

2,684
24
31

This is in fact a Rails application, I was afraid that that the `unless const_defined?` is a solution that masks the problem and not actually solves it. – Nov 08 '11 at 09:39
2

If the problem is source reloading, then this masks it. Otherwise, it solves it. :-) – sheldonh Nov 08 '11 at 11:20

score 5 · Answer 3 · answered Apr 06 '15 at 22:09

5

RESET is not a constant if it keeps changing in your code. If you rename it to lower case 'reset', the problem disappears. Ruby thinks Upper case variables are constants and thus displays an error to warn you that a constant has changed.

answered Apr 06 '15 at 22:09

Luis Pizana

91
1
1

I am just running "knife client list". I dunno or modifying any variable – Satish Patro Jun 20 '19 at 13:48

score 0 · Answer 4 · answered Jul 06 '23 at 17:09

0

Try bundle clean --force and then bundle update

answered Jul 06 '23 at 17:09

N7Dev

1

solutions to the annoying "warning: already initialized constant" message

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