Upon first reading this, I thought, "what's the difference?" More to the point, "how does one behave differently from the other?" After all, an empty string in a numeric context is zero anyway. How would one ever see the difference?

Some time later, the answer popped into my head. A string turned number will trigger warnings, but s/// won't. I verified this in the Test::More fashion. 

use strict;
use warnings;

use Test::More 'tests' => 7;

sub empty_string { '' }
sub no_replacement { my $x = 'x'; return ($x =~ s/y//); }

my $warning;
$SIG{__WARN__} = sub { $warning = shift };

ok( ! defined $warning, 'no warning recorded' );
is( 0+empty_string(), 0, 'empty string is zero' );
ok( $warning, 'warning is generated' );
my $expected_warning = q{Argument "" isn't numeric in addition (+)};
is( substr( $warning, 0, length $expected_warning ),
    $expected_warning,
    q{warning is the one that's expected} );

undef $warning;
ok( ! defined $warning, 'recorded warning is cleared' );
is( 0+no_replacement(), 0, 'no replacement is zero' );
ok( ! defined $warning, 'no warning is generated' );

[download]

Thanks for the food for thought.

In reply to Re^4: Newbie: parentheses, map, etc. by kyle
in thread Newbie: parentheses, map, etc. by nefigah

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