How to disable warning for redefining a constant when loading a file

Question

Is there a way to disable warning: already initialized constant when loading particular files?

Warnings are often indicative of non-fatal **errors**, and should be fixed. In this case you do very possibly have a real problem that should be fixed. — Andrew Marshall, Feb 10 '12 at 23:29
@DmitrySavy Yes. That's right. But that does not answer my question. — sawa, Feb 10 '12 at 23:35
possible duplicate of [How to redefine a Ruby constant without warning?](http://stackoverflow.com/questions/3375360/how-to-redefine-a-ruby-constant-without-warning) — the Tin Man, Feb 10 '12 at 23:36
@theTinMan Thanks. I think your link tells my what I need to do. But still, I would like to do it without using special methods mentioned there. — sawa, Feb 10 '12 at 23:40

user2398029 · Answer 1 · 2014-06-12T01:17:26.297

The solution to your problem depends on what is causing it.

1 - You are changing the value of a constant that was set before somewhere in your code, or are trying to define a constant with the same name as an existant class or module. Solution: don't use constants if you know in advance that the value of the constant will change; don't define constants with the same name as class/modules.

2 - You are in a situation where you want to redefine a constant for good reasons, without getting warnings. There are two options.

First, you could undefine the constant before redefining it (this requires a helper method, because remove_const is a private function):

Object.module_eval do
  # Unset a constant without private access.
  def self.const_unset(const)
    self.instance_eval { remove_const(const) }
  end
end

Or, you could just tell the Ruby interpreter to shut up (this suppresses all warnings):

# Runs a block of code without warnings.
def silence_warnings(&block)
  warn_level = $VERBOSE
  $VERBOSE = nil
  result = block.call
  $VERBOSE = warn_level
  result
end

3 - You are requiring an external library that defines a class/module whose name clashes with a new constant or class/module you are creating. Solution: wrap your code inside a top-level module-namespace to prevent the name clash.

class SomeClass; end
module SomeModule
   SomeClass = '...' 
end

4 - Same as above, but you absolutely need to define a class with the same name as the gem/library's class. Solution: you can assign the library's class name to a variable, and then clear it for your later use:

require 'clashing_library'
some_class_alias = SomeClass
SomeClass = nil
# You can now define your own class:
class SomeClass; end
# Or your own constant:
SomeClass = 'foo'

score 32 · Answer 2 · answered Dec 29 '13 at 17:33

32

Try this :

Kernel::silence_warnings { MY_CONSTANT = 'my value '}

answered Dec 29 '13 at 17:33

NNA

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4

This method doesn’t exist with Ruby 2.0.0. – bfontaine Feb 05 '14 at 15:52
9

It's a part of rails: http://api.rubyonrails.org/classes/Kernel.html#method-i-silence_warnings – stackdump Apr 18 '14 at 00:38
2

Excellent solution, It's part of rails, but you can just import the 2 methods `silence_warnings` and `with_warnings` in a file of your choice and patch `Kernel` with it. – Benjamin Bouchet Feb 08 '15 at 01:32
2

If you are using Rails, this is probably what you want. – Kyle Heironimus Mar 20 '18 at 21:41
And you can use it without `Kernel::` prefix, it'll be even shorter then! – Lev Lukomsky Jul 13 '18 at 08:31

score 18 · Accepted Answer · edited Sep 24 '13 at 11:10

18

To suppress warnings, use the following code at the top of the script:

$VERBOSE = nil

edited Sep 24 '13 at 11:10

Lundin

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answered Sep 24 '13 at 10:49

Bharat

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1

This one is the most useful for other people in the broader context, because Constant redefinition is only one thing that can trigger non-fatal compilation warnings. It's all very well suggesting you fix your code, but that presumes the thing triggering this is in your code and not something in an upstream library. – Stuart Harland Jul 31 '19 at 09:44
yes, that works, but silencing *all* warnings is maybe not the best in production – Tilo Jan 12 '22 at 21:54

score 15 · Answer 4 · edited May 23 '17 at 12:26

15

The accepted answer to this question was helpful. I looked at the Rails source to get the following. Before and after loading the file, I can insert these lines:

# Supress warning messages.
original_verbose, $VERBOSE = $VERBOSE, nil
    load(file_in_question)
# Activate warning messages again.
$VERBOSE = original_verbose

edited May 23 '17 at 12:26

Community

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1

answered Feb 10 '12 at 23:57

sawa

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that worked. I should probably write a wrapper for it. – Dorian Oct 13 '14 at 22:39

score 0 · Answer 5 · answered Dec 15 '22 at 10:28

0

Using user2398029's reply the simplest way for me to remove warnings was to add this line:

before { described_class.instance_eval { remove_const(:CONSTANT_NAME) } }

answered Dec 15 '22 at 10:28

Samuel-Zacharie Faure

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How to disable warning for redefining a constant when loading a file

5 Answers5