Closed
Description
The following code unexpectedly invokes the tied FETCH function twice on every iteration line. If instead the code returned a non-overloaded object then this only happens once.
use v5.14;
use warnings;
package BoldStars {
use overload
'""' => sub {
my $self = shift; ## <-- THIS is line 7
my $str = $self->[0];
# Wrap every word in *stars*
return $str =~ s/(\S+)/*$1*/gr;
},
fallback => 1;
sub new {
my $class = shift;
my $self = bless [ $_[0] ], $class;
return $self;
}
}
package TiedCounter {
use Carp;
my $dashes = "";
sub TIESCALAR {
my $class = shift;
return bless [], $class;
}
sub FETCH {
carp "FETCHing TiedCounter";
$dashes .= "-";
return BoldStars->new( $dashes );
}
}
tie my $tiecounter, "TiedCounter";
say $tiecounter for 1 .. 5; ## <-- THIS is line 37
I'd expect it to print 5 rows of output with each one having one more dash than the prior:
*-*
*--*
*---*
*----*
*-----*
but instead it prints:
FETCHing TiedCounter at tie-fetch-twice.pl line 37.
FETCHing TiedCounter at tie-fetch-twice.pl line 7.
*--*
FETCHing TiedCounter at tie-fetch-twice.pl line 37.
FETCHing TiedCounter at tie-fetch-twice.pl line 7.
*----*
FETCHing TiedCounter at tie-fetch-twice.pl line 37.
FETCHing TiedCounter at tie-fetch-twice.pl line 7.
*------*
FETCHing TiedCounter at tie-fetch-twice.pl line 37.
FETCHing TiedCounter at tie-fetch-twice.pl line 7.
*--------*
FETCHing TiedCounter at tie-fetch-twice.pl line 37.
FETCHing TiedCounter at tie-fetch-twice.pl line 7.
*----------*
The FETCH function really was run twice for each call. Each row has two more dashes than the prior. The FETCH call from line 37 was expected, the one from lines 7 was most certainly not.
If you remove the use overload ... declaration then this goes away and only runs once (and overloading no longer happens of course):
FETCHing TiedCounter at tie-fetch-twice.pl line 37.
BoldStars=ARRAY(0x556a4784bf70)
FETCHing TiedCounter at tie-fetch-twice.pl line 37.
BoldStars=ARRAY(0x556a4784b4d8)
FETCHing TiedCounter at tie-fetch-twice.pl line 37.
BoldStars=ARRAY(0x556a4784c210)
FETCHing TiedCounter at tie-fetch-twice.pl line 37.
BoldStars=ARRAY(0x556a47858a78)
FETCHing TiedCounter at tie-fetch-twice.pl line 37.
BoldStars=ARRAY(0x556a4781e8c0)