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Id: 1085
Status: resolved
Priority: 0/
Queue: perl5

Owner: Nobody
Requestors: ilya [at] math.ohio-state.edu
Cc:
AdminCc:

Operating System: generic
PatchStatus: (no value)
Severity: medium
Type:
Perl Version: (no value)
Fixed In: (no value)



From: Ilya Zakharevich <ilya [...] math.ohio-state.edu>
Date: Tue, 27 Jul 1999 17:16:11 -0400 (EDT)
To: thorfinn [...] netizen.com.au, perlbug [...] perl.com
Subject: Re: what should be output of perl -we 'print do { foreach (1, 2) { 1; } }'?
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If this were true, then Show quoted text
>perl -we "print do { 17; foreach (1,2) { 1; } }"
would print 17. But it prints Useless use of a constant in void context at -e line 1. I consider this (no return of foreach) as a bug, and report it as such. Ilya
Subject: what should be output of perl -we 'print do { foreach (1, 2) { 1; } }'?
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If Data::Dumper is to be believed, it returns an empty string. $ perl -MData::Dumper -wle "@a = do { foreach (1,2) { 1; } }; print Dumper \@a" $VAR1 = [ '' ]; Different from an empty do block. $ perl -MData::Dumper -wle "@a = do { }; print Dumper \@a" $VAR1 = []; This explains why do { 17; foreach ... } complains about a useless constant. A while loop returns 0. $ perl -MData::Dumper -wle '$foo = 42; sub foo { $bar = 2; $foo++; while ($bar--) { 1; } } print Dumper [foo]' $VAR1 = [ 0 ]; Changing this behavior can cause serious backwards compat issues. Consider the options: 1) Have foreach be "null" so the statement before it is what is returned from the block. That will alter subroutines such as: sub foo { $foo++; foreach (...) { ... } } Currently this will return an empty string. If we change the foreach behavior, it will return the value of $foo. 2) Have foreach return its last evaluated expression in its block. Similar problem. Any subroutine ending in a foreach loop will suddenly start returning values. I suppose it should be documented, but at this point it would likely be better to simply declare it undefined rather than paint ourselves into a corner by documenting that it returns false. Perhaps to say simply that for purposes of the "last evaluated expression" rule, a loop is an expression and its value is undefined.
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On Tue Jul 15 19:20:10 2003, schwern wrote: Show quoted text
> A while loop returns 0.
Actually, that has changed: in my perl-5.10.0, while loop returns an empty string as well. So the situation is more consistent now. It's almost ten years since the ticket was started, almost 6 years since it was noted that foreach returns an empty string. Let's call it a tradition and close the ticket.


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