On Thu, Jul 15, 2010 at 09:52, Dr.Ruud <[email protected]> wrote:
> Bryan R Harris wrote:
>
>> Out of curiosity, is there a unary not operator in perl?
>>
>> i.e. "$a = $a+1" is the same as "$a++"
>>
>> Is there a similarly short form of "$a = !$a"? Like "$a!!"? (tried it
>> and
>> it didn't work.)
>
> perl -wle '
> print --$| for 1..4;
> '
> 1
> 0
> 1
> 0
snip
Interesting behavior. That isn't documented in perlvar. I assume
what is happening is that $| sets itself to 1 whenever a non-zero
value is assigned to it:
perl -le '$| = 20; print $|'
perl -le '$| = -1; print $|'
The first --$| is $| = $| - 1 or $| = 0 - 1 or $| = -1. Since -1 is
nonzero $| becomes 1, the second --$| is $| = $| = $| - 1 or $| = 1 -
1 or $| = 0. Since 0 is zero, $| becomes 0. You can generated this
same behavior with a tied scalar:
#!/usr/bin/perl
use strict;
use warnings;
#Don't do this, it is silly.
{ package Silly;
sub TIESCALAR { bless \my $self, shift }
sub FETCH { ${+shift} }
sub STORE {
my ($self, $val) = @_;
$$self = 0+!!$val;
}
}
tie my $silly, "Silly";
print --$silly, "\n" for 1 .. 4;
--
Chas. Owens
wonkden.net
The most important skill a programmer can have is the ability to read.
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