Prev: Confusion about the smart matching operator
Next: FAQ 5.19 How can I open a file with a leading ">" or trailing blanks?
From: sln on 25 Jul 2010 16:56
On Fri, 23 Jul 2010 09:40:06 -0700 (PDT), Dilbert <dilbert1999(a)gmail.com> wrote:

>In perl 5.12.1, with reference to the exist function "perldoc -f
>exist" ( see also http://perldoc.perl.org/functions/exists.html ) it
>says
>
>>> [...]
>>> Although the mostly deeply nested array or hash will
>>> not spring into existence just because its existence
>>> was tested, any intervening ones will. Thus $ref->{"A"}
>>> and $ref->{"A"}->{"B"} will spring into existence due to
>>> the existence test for the $key element above.
>>> [...]
>>> This surprising autovivification in what does not at first
>>> --or even second-- glance appear to be an lvalue context
>>> may be fixed in a future release.
>
>Has this particular case of surprising autovivification always
>existed, even in perl 5.10 or 5.8 ?


This may be a workaround (suprisingly nitpicky to do).

-sln
-------------------

use strict;
use warnings;
use Data::Dumper;

my $x;
$x->{''}{''}{2} = '';
$x->{a} {''}{c}{d} = undef;
print Dumper( $x );

print "1> pass = ", scalar deep_exists( $x, 'a', undef, 'c'), "\n";
print "2> pass = ", scalar deep_exists( $x, '' , undef), "\n";
print "3> pass = ", scalar deep_exists( $x, '' , undef, '2', ''), "\n";

my ($pass, $found) = deep_exists($x, 'a', '', 'c', 'd');
print "4> pass = $pass, found = $found\n";
print "5> pass = ", scalar deep_exists( $x), "\n";
print "6> pass = ", scalar deep_exists(), "\n";
exit 0;

##
sub deep_exists {
return (0,0) unless @_;
my $t = shift;
my $count = map {
my $key = $_ // '';
( ref($t) eq "HASH" and exists $t->{$key} )
? $t = $t->{$key}
: ()
} @_;
my $res = (@_ && $count == @_) ? 1 : 0;
return wantarray ? ($res, $count) : $res;
}

From: Ilya Zakharevich on 25 Jul 2010 17:08
On 2010-07-25, Willem <willem(a)turtle.stack.nl> wrote:
> ) For each person for whom it is not surprising, how many for which it is?

> For each person for whom it is surprising, how many for which it is not?

0, up to experiment's errors. But you know this already; why ask?

Puzzled,
Ilya
First  |  Prev  | 
Pages: 1 2 3
Prev: Confusion about the smart matching operator
Next: FAQ 5.19 How can I open a file with a leading ">" or trailing blanks?