How does this code work (warnings.pm)?

John M. Dlugosz has asked for the wisdom of the Perl Monks concerning the following question:

given

use warnings; # implies 'all'
use Some::Module;  # does a warnings::register
Some::Module::badcall();
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The call to badcall() will see that that module's warnings are enabled. Looking at the code in use warnings and use warnings::register, I see that adding a category will extend the mask for 'all' to include the new bit, but it can't do a thing about the existing values of ${^WARNING_BITS}. Shouldn't that new bit still be off in this scope?

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Re: How does this code work (warnings.pm)? by chromatic (Archbishop) on Aug 08, 2002 at 19:42 UTC
If I understand your question correctly, you are asking why enabling all warnings doesn't enable warnings that don't exist yet? I think it's because it doesn't know what warnings will exist until they do exist. That doesn't mean I think it's an unreasonable idea, just that the current implementation makes it a little tricky. This is a core module, so any proposals to change it should be directed to p5p.	[reply]
Re: Re: How does this code work (warnings.pm)? by John M. Dlugosz (Monsignor) on Aug 08, 2002 at 20:22 UTC
No, I found emperically that it does enable warnings that don’t exist yet, and I don’t see how that’s happening. The code looks like it should, like you say, be unaware of them and they are created as off. —John	[reply]