Does perl have an internal function to unquote a variable?

Question

It is not uncommon that a parameter is passed a few times.

Here is an interesting example of losing the quote can actually helps.

The first abs() return a variable without quote, making the second abs return the correct value.

My question is:

Does perl have an internal function to unquote a variable so that I do not have to code this way?

#!/usr/bin/perl -w
use strict;
my @nums = (
    '-0',
    '-0.0',
    "-0.000",
    qw(-0.000),
    sprintf("%.4f", "-0.0"),
);

print "***use single abs()\n";
foreach my $num(@nums){
    my $number = $num;
    my $abs = abs($number);
    print "<$num> abs <$abs>\n";
}

print "\n***use abs(abs())\n";
foreach my $num(@nums){
    my $abs_abs = abs(abs($num));
    print "<$num> double abs <$abs_abs>\n";
}

System information:

uname -r
2.6.32-573.12.1.el6.centos.plus.x86_64
This is perl, v5.10.1 (*) built for x86_64-linux-thread-multi

The screen output:

***use single abs()
<-0> abs <0>
<-0.0> abs <-0>
<-0.000> abs <-0>
<-0.000> abs <-0>
<-0.0000> abs <-0>

***use abs(abs())
<-0> double abs <0>
<-0.0> double abs <0>
<-0.000> double abs <0>
<-0.000> double abs <0>
<-0.0000> double abs <0>

Answer 1

That's not an issue with quotes -- the quotes are just Perl syntax to tell the interpreter where a string begins and ends. Perl knows that the value being stored is a string, but the quotes themselves are not stored in memory.

Rather, it's an artifact of the special floating point value "-0.0". For almost any use, it is equivalent to the value 0.0

perl -E ' $p = 0.0; $n = -0.0; say $p == $n '                    ==> 1
perl -E ' $p = 0.0; $n = -0.0; $x = 4.2; say $p+$x == $n+$x '    ==> 1

The two exceptions, as far as I can tell, are their binary representation and their string representation.

$ perl -e 'print pack "F",0.0' | od -c
0000000  \0  \0  \0  \0  \0  \0  \0  \0
0000010
$ perl -e 'print pack "F",-0.0' | od -c
0000000  \0  \0  \0  \0  \0  \0  \0 200
0000010

$ perl -MDevel::Peek -e 'Dump($n=-0.0),Dump($p=0.0)'
SV = NV(0x43523d8) at 0x434ff00
  REFCNT = 1
  FLAGS = (NOK,pNOK)
  NV = -0
SV = NV(0x43523e0) at 0x4329b58
  REFCNT = 1
  FLAGS = (NOK,pNOK)
  NV = 0

$ perl -E '$p=0.0; $n=-0.0; say for $p,$n'
0
-0

(actually, with Perl v5.12 I see 0,-0 but with v5.16 it is 0,0 -- maybe somebody noticed this and fixed it)

The integers 0 and -0 do not have this issue. abs(-0.0) returns the integer 0, and so it really by accident that abs appears to resolve this "quoting" issue.