Re: Why does $$self++ works?

[davido]

This is a blessed scalar. Something like this:

sub new {
    my ($class, $initial_int) = @_;;
    my $scalar = 0+($initial_int // 0);
    return bless \$scalar, $class;
}

A more typical constructor would bless a hashref:

sub new {
    my ($class, $args) = @_;
    die "Constructor args must be passed as a hash reference.\n"
        if defined($args) && ref($args) ne 'HASH';
    $args //= {};
    return bless $args, $class;
}

(Neither of these have a sufficient level of error checking on their input paramaters, and are intended as a demonstration only.)

But we'll look at the blessed scalar reference, as it's what is probably at play here. The last piece is this:

my $o = Foo->new(0);
${$o}++; # dereference $o, then increment the value of the scalar that
+ the scalar reference in $o points to.

# Because the dereferencing sigil binds more closely than the postincr
+ement operator, you can also do this:
$$o++; # dereference $o, then increment the value of the scalar that t
+he scalar reference in $o points to.