One may say that this effect may be avoided by remembering to carefully localize all package variables in all called functions,

Unintended side effects are unintended side effects:

sub G { our @ydata = 'Gaaaahh!'; };;
sub F{ 
    my @a = @_; 
    print qq{pre-G: (@ydata)}; 
    G(); 
    print qq{post-G: (@ydata)}; 
};;

F(1..4);;
pre-G: ()
post-G: (Gaaaahh!)

[download]

The problem has nothing to do with aliasing and everything to do with not localising!

Your previous quote is better stated as: "don't use code that uses globals for no good reason.".

Which is doubly true for code that fails to localise its use of globals.

a healthy dose of paranoia.

Sorry, but I will always consider 'paranoia' in programming -- and pretty much everything else for that matter -- with exclusively negative connotations.

The teaching of 'paranoia', rather than 'knowledge', in an attempt to avert disaster, is always a counter productive and ultimately futile process.

With paranoia, one can only hope to avert bad consequences; with knowledge one can know you have.

Don't hope, know!

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

In reply to Re^4: aliasing arrays using typeglob under strict by BrowserUk
in thread aliasing arrays using typeglob under strict by RockyMtn

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