in reply to Re^2: ref to read-only alias ... why? (notabug)
in thread ref to read-only alias ... why?

I'd document it pretty much as I already described it. Passing a read-only value or a literal constant to something that makes aliases (for, a sub) may decide to make an alias to the read-only value or may decide to make a copy of it. The decision might even be different in those two case (a literal constant vs. some other read-only scalar). The choice is a matter of optimization and subtle edge cases and Perl code should not depend on either specific behavior. Both behaviors have existed in many different versions of Perl.

No, I don't consider it a bug that some versions of Perl don't die in the face of: 

sub add1 { return ++$_[0]; }
my $two= add1(1);

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Despite the use of "++" over "1+" there being questionable. It does have the interesting and perhaps useful side effect of allowing: add1($count). Yes, it is a contrived example. As is yours.

I don't find it hard to imagine cases where either result would be preferred. I do find it hard to imagine cases where either result is a serious problem that I wouldn't just address with a better interface for the subroutine.

- tye        

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Re^4: ref to read-only alias ... why? (notabug)
by dk (Chaplain) on Jan 06, 2012 at 17:07 UTC
    Thanks for commenting. Here's a case with a serious problem: a person writes code that doesn't fail, which then gets executed on another installation, and fails. I'd say it's bad enough. I believe I'd file a bug after all (unless you have reasons for me not to).
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      Wow. To have code that runs fine for the author and then fails somewhere else constitutes a "serious problem" to you? Cushy world you must've lived in before. Ever looked at "cpan testers" reports? *shrug*

      I wouldn't file a bug. I'd rather just add an eval to the code (actually, I'd probably make a less fragile interface to the sub, as I said).

      - tye        

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        > less fragile interface to the sub

        We showed that any call-by-reference can be affected.

        So you are effectively saying that modifying $_[ ] is a fragile interface and bad coding practice?

        I agree it's not a crisis, but this must at least be documented, not only for helping people desperately trying to understand the reason why an imported sub using another imported sub fails out of a sudden, because an alias was passed thru the chain.

        This can't be avoided, even less if people use Data::Alias or Lexical::Alias.

        UPDATE:

        > I'd rather just add an eval to the code

        And how do you expect eval to help if there is no error thrown?

        Cheers Rolf

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[d/l]
        I'd be grateful if you wouldn't be sarcastic towards me, I hate that. I'd continue to collaborate, but I'd think that you're an idiot. Thanks otherwise for expressing your opinion.
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