Re^3: Elegant way to return true or nothing from a subroutine?

Ignoring non-integer values for brevity, the not not transformation maps 0 to 0 and everything else to 1:

my @nums = (-2 .. 2);
for my $num (@nums) {
    printf "!!%2d => %d\n", $num, !!$num;
}
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gives

!!-2 => 1
!!-1 => 1
!! 0 => 0
!! 1 => 1
!! 2 => 1
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Re^4: Elegant way to return true or nothing from a subroutine? by ikegami (Patriarch) on Oct 10, 2006 at 16:22 UTC
Not quite. The `not not` transformation maps 0 to false and every other integer to 1. False acts as the nul string in string context, and acts as zero in numerical context. `use warnings; my $false = !!0; my $numzero = 0; my $strzero = '0'; my $nulstr = ''; local $\ = "\n"; print 'false: ', $false; # '' <-- Not zero! print '0: ', $numzero; # '0' print "'0': ", $strzero; # '0' print "'': ", $nulstr; # '' print ''; print 'false: ', 0+$false; # '0' (no warning) print '0: ', 0+$numzero; # '0' (no warning) print "'0': ", 0+$strzero; # '0' (no warning) print "'': ", 0+$nulstr; # '0' with warning` [download] If you wanted something that maps 0 to 0 and every other integer to 1, you'd want `0 + !!$var`. Update: Added $strzero. Minor cosmetic changes.	[reply] [d/l] [select]

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Re^4: Elegant way to return true or nothing from a subroutine?
by ikegami (Patriarch) on Oct 10, 2006 at 16:22 UTC

not not

false

use warnings;

my $false   = !!0;
my $numzero = 0;
my $strzero = '0';
my $nulstr  = '';

local $\ = "\n";

print 'false: ', $false;      # ''  <-- Not zero!
print '0:     ', $numzero;    # '0'
print "'0':   ", $strzero;    # '0'
print "'':    ", $nulstr;     # ''

print '';

print 'false: ', 0+$false;    # '0' (no warning)
print '0:     ', 0+$numzero;  # '0' (no warning)
print "'0':   ", 0+$strzero;  # '0' (no warning)
print "'':    ", 0+$nulstr;   # '0' with warning
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If you wanted something that maps 0 to 0 and every other integer to 1, you'd want 0 + !!$var.

Update: Added $strzero. Minor cosmetic changes.

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