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Postings from November 1999
Martyn Pearce <m.pearce@inpharmatica.co.uk> wrote > Hence the while loop assigns to $_ which is an alias into @array. No > surprise. But you haven't pointed out the key issue, that while never localises any variable, unlike foreach. And this point isn't stressed in the current (5.005_03) documentation. The development version (5.005_62) makes this more explicit: ---------------------pod/perlop.pod-------------------- Ordinarily you must assign the returned value to a variable, but there is one situation where an automatic assignment happens. If and only if the input symbol is the only thing inside the conditional of a C<while> statement (even if disguised as a C<for(;;)> loop), the value is automatically assigned to the global variable $_, destroying whatever was there previously. (This may seem like an odd thing to you, but you'll use the construct in almost every Perl script you write.) The $_ variables is not implicitly localized. You'll have to put a C<local $_;> before the loop if you want that to happen. ------------------------------------------------------- I think the attached patch to perlsyn would also be useful. Mike Guy --- ./pod/perlsyn.pod.orig Fri Sep 17 21:23:08 1999 +++ ./pod/perlsyn.pod Fri Nov 26 16:02:15 1999 @@ -163,6 +163,8 @@ refers to the innermost enclosing loop. This may include dynamically looking back your call-stack at run time to find the LABEL. Such desperate behavior triggers a warning if you use the B<-w> flag. +Unlike a C<foreach> statement, a C<while> statement never implicitly +localises any variables. If there is a C<continue> BLOCK, it is always executed just before the conditional is about to be evaluated again, just like the third part of a End of patch