In Perl 5:

package MyClass;

our $total_objects;
our $public_static_class_data;
my $private_static_class_data;

# For example:
sub new {
   # ...
   $total_objects++;
   # ...
}
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In Perl 6, the above would work if you replace package with class (though in general you don't write a new method yourself in Perl 6).