Backslash before a subroutine call - perl

Question

As I was understanding the difference between [] and \ in references,I used both on subroutine the former was fine but when I tried later I thought it should give error but the below program in perl
#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
my #b;
for my $i ( 0 .. 10 ) {
$b[$i] = \somefunc($i);
}
print Dumper( \#b );
sub somefunc {
my $n = shift;
my ( #a, $k );
for my $j ( 11 .. 13 ) {
$k = $n * $j;
push( #a, $k );
}
print "a: #a \n";
return #a;
}
gives output as :
a: 0 0 0
a: 11 12 13
a: 22 24 26
a: 33 36 39
a: 44 48 52
a: 55 60 65
a: 66 72 78
a: 77 84 91
a: 88 96 104
a: 99 108 117
a: 110 120 130
$VAR1 = [
\0,
\13,
\26,
\39,
\52,
\65,
\78,
\91,
\104,
\117,
\130
];
I was unable to understand the output.Need explanation.

Answer 1

What is happening here is:
You are returning an array from somefunc.
But you are assigning it to a scalar. What this is effectively doing therefore, is simply putting the last value in the array, into the scalar value.
my $value = ( 110, 120, 130 );
print $value;
When you do this - $value is set to the last value in the array. This is what's actually happening in your code. See for example perldata:
List values are denoted by separating individual values by commas (and enclosing the list in parentheses where precedence requires it):
(LIST)
In a context not requiring a list value, the value of what appears to be a list literal is simply the value of the final element, as with the C comma operator. For example,
#foo = ('cc', '-E', $bar);
assigns the entire list value to array #foo, but
foo = ('cc', '-E', $bar);
assigns the value of variable $bar to the scalar variable $foo. Note that the value of an actual array in scalar context is the length of the array; the following assigns the value 3 to $foo:
#foo = ('cc', '-E', $bar);
$foo = #foo; # $foo gets 3
It's this latter case that's often the gotcha, because it's a list in a scalar context.
And in your example - the backslash prefix denotes 'reference to' - which is largely meaningless because it's a reference to a number.
But for a scalar, it might be more meaningful:
my $newvalue = "fish";
my $value = ( 110, 120, 130, \$newvalue );
print Dumper $value;
$newvalue = 'barg';
print Dumper $value;
Gives:
$VAR1 = \'fish';
$VAR1 = \'barg';
That's why you're getting the results. Prefix with the slash indicates that you're getting a reference to the result, not a reference to the sub. Reference to 130 isn't actually all that meaningful.
Normally, when doing the assignment above - you'd get a warning about Useless use of a constant (110) in void context but this doesn't apply when you've got a subroutine return.
If you wanted to insert a sub reference, you'd need to add &, but if you just want to insert the returned array by reference - you either need to:
$b[$i] = [somefunc($i)]
Or:
return \#a;