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Re: [perl #114178] di/ds/ig exempt from warnings in void context

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Leon Timmermans
July 18, 2012 11:39
Re: [perl #114178] di/ds/ig exempt from warnings in void context
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On Wed, Jul 18, 2012 at 4:35 PM, Paul Johnson <> wrote:
> On Tue, Jul 17, 2012 at 11:44:35PM -0700, wrote:
>> % perl -we '"qwertasd"'
>> Useless use of a constant ("qwertasd") in void context at -e line 1.
>> % perl -we '"dsatrewq"'
>> Any string starting with "di", "ds", or "ig" is exempt from "void context"
>> warnings. I can't find any documentation for this misfeature. It should be
>> removed from the interpreter.
> It's not really a misfeature.  It's more of an old feature.  The code
> explains why it's there:
> op.c:1473
>                   /* perl4's way of mixing documentation and code
>                      (before the invention of POD) was based on a
>                      trick to mix nroff and perl code. The trick was
>                      built upon these three nroff macros being used in
>                      void context. The pink camel has the details in
>                      the script wrapman near page 319. */
> As far as documentation is concerned, I suppose that it wouldn't be a
> bad thing to make a note of this somewhere.
> As far as removing it is concerned, I presume that no one is writing new
> code in this way, and probably hasn't for a few years.  So the removal
> is a trade-off between a slight standardisation and simplification and
> breaking backwards compatibility with some perl4 era programs.
> I would side with keeping backwards compatibility.

Considering this is a warning that has to be enabled explicitly, and
that we're talking about perl 4 compatibility here, I wouldn't care
too much about such a minor break of backwards compatibility. I'd be
surprised if this was the first time in the past 18 years that such a
thing happened.


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