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Re: About "state" variables in Perl 5.10

by exussum0 (Vicar)
on Dec 28, 2007 at 18:46 UTC ( #659376=note: print w/ replies, xml ) Need Help??


in reply to About "state" variables in Perl 5.10

Neat. C style static variables. I do have one curious thought. Didn't oop solve this via objects/classes? Was there a great demand for it? What inspired this neat little feature?


Comment on Re: About "state" variables in Perl 5.10
Re^2: About "state" variables in Perl 5.10
by grinder (Bishop) on Dec 28, 2007 at 22:30 UTC

    One particular itch that needed scratching, apart from some of the points that TimToady makes, is that it got rid of the ugly state-with-a-my hack that went something like:

    my $persist if 0;

    That particular construct breaks through the abstraction of the language and hits an oddity in the way lexicals are implemented. The result of which was, when used in a routine, a variable that maintained its previous value next time the routine was called.

    It was a sufficiently desirable trick that it was independently discovered time and again, by people who understood the language sufficiently deeply, and tried it out and were happy to discover that it worked.

    Unfortunately, it was also regularly discovered by people who had no idea what was going on, and it led to bugs that were difficult to understand and fix (especially when the if 0 was buried under a complex expression).

    So one of things that went into 5.10 was the outlawing of my $foo if 0 to stop people shooting themselves in the foot, and the introduction of state variables, for those who needed them.

    • another intruder with the mooring in the heart of the Perl

      So one of things that went into 5.10 was the outlawing of my $foo if 0

      Why still allow my $foo if $bar; ? Such seems, if anything, worse than the if 0 construct. I can understand putting it through a deprecation cycle but not even that was started.

      - tye        

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