sub PUSH {
  my ($aref, @new) = @_;

  carp "first parameter must be an array reference" unless ref $aref eq 'ARRAY';
  ...
}

##</code><code>##

sub NAMED_PUSH {
  my(%args) = @_;

  carp "dest_aref parmeter must be an array reference" unless ref $args{dest_aref} eq 'ARRAY';
  ...
}