my %hash ;
  
  tie(%hash , 'TiedHash') ;
  
  print "key: $hash{key}\n" ;
  
  if ( %hash ) { print "BOOL: 1\n" ;}
  else { print "BOOL: 0\n" ;}

package TiedHash ;

  use overload (
  'bool' => sub{ print "OVER1!\n" ; } , ## print() return 1!
  '""' =>   sub{ print "OVER2!\n" ; } ,
  '0+' =>   sub{ print "OVER3!\n" ; } ,  
  'fallback' => 1 ,
  );

sub TIEHASH { bless({}, __PACKAGE__ ) ;}

sub FETCH { return( 'fetch_val' ) ;}


##</code><code>##

  my %hash = (1) ;
  
  tie(%hash , 'TiedHash') ;
  
  if ( %hash ) { print "BOOL: 1\n" ;}
  else { print "BOOL: 0\n" ;}

package TiedHash ;

sub TIEHASH { bless({}, __PACKAGE__ ) ;}