Usecase of an reference to scalar in perl?

Question

I'm learning perl references, I understand the usefullness of the references to hases or arrays. But thinking about in what scenarios can be useful a reference to an scalar value.

my $x = 1;
my $sr = \$x;

where can be useful to use $$sr, instead of direct use of $x?

For example, when traversing any deep hashref structure, isn't the common practice returning a reference if the given node is hashref or arrayref, but returning directly the scalar value instead of returning a reference to the scalar?

Exists some functions or modules what uses or return references to scalars, instead of returning the scalar's value?

Answer 1

In a subroutine, when you want to directly modify the values being passed into it.

e.g.

sub increment_this {
     my ( $inc_ref ) = @_;
     ${$inc_ref}++;
}  

Bit of a trivial case I know, but perhaps more pertinent would be examples like chomp which removes trailing letters from a variable or $_.

If you think about it though - $_ is often effectively a reference. If you do this:

my @array = qw ( 1 2 3 );
foreach ( @array ) {
    $_++;
}

print @array; 

Modifying $_ has modified the contents of the array.