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Closures are cloned, unlike with L<Clone|Clone>. Closed-over lexicals
will be cloned if they were originally declared in a scope that could be
run more than once, and shared otherwise. 

That is, in the example in the
L</SYNOPSIS>, $count is cloned as it is scoped to &count, which can run
many times with different $count variables; but $total is shared as it
is file-scoped, so there will only ever be one copy. 

Generally speaking, C<clone> will produce what might have been another
copy of the closure, generated by the same means. However, see L</BUGS>
below.

=head2 Magic

The following types of magic are preserved:

=over 4

=item *

shared variables

Cloning a shared variable creates a new shared variable, but it is not
shared with any other threads yet. That is, the clone is only visible in
this thread and any threads you create later.

=item *

tied variables

The tied object will also be cloned.

=item *

C<qr//> compiled regexes

=item *

tainted values

Cloning a tainted value produces a tainted copy.

=item *

globs

Globs are not cloned. Cloning a glob returns the original glob.

=item *

weakrefs

Beware cloning weakrefs: cloning a reference also clones the object it
refers to, and if there are no strong refs to this new object it will
self-destruct before C<clone> returns. For example,

    my $sv  = 5;
    my $ref = \$sv;
    weaken $ref;
    my $clone = clone $ref;

will result in $clone being C<undef>, as the new clone of $sv has no
(strong) referents. As weakrefs are normally used to break loops in
self-referential structures, this should not happen often.

=item *

custom magic (C<U>, C<u>, and C<~> magics)

These will be cloned, and if the magic has a C<mg_obj> that will be
cloned too. This is not necessarily the right thing to do, depending on
what the custom magic is being used for.

=item *

Boyer-Moore fast string search

=item *

vstring magic

=item *

UTF8 cache magic

These types of magic are not visible from Perl-space, and are used by
perl to optimize certain operations.

=back

All other types of magic are dropped when cloning, so for example

    my $env = clone \%ENV;

will produce a normal hashref containing a copy of the environment.

=head1 BUGS

=head2 Loops

Loops are currently not correctly recognized as 'scopes that may run
more than once'. That is, given

    my @subs;

    for my $i (1..10) {
        push @subs, sub { $i };
    }

a clone of $subs[0] will B<share> $i, which is probably not what you
wanted. One possible workaround is to generate the closure in a sub,
with its own lexical; for example

    my @subs;

    sub make_closure {
        # this is important, so we get a new lexical
        my $i = shift;