use strict;

my %hash = (
    apple   => 'pie',
    banana  => 'custard',
    cherry  => 'ripe',
  );

# use map to alternate $delim between = and ,
my $delim = '';
my $str = join $delim, map { $delim = ($delim eq ',' ? '=' : ','); $_ } %hash;
print "result: [$str]\n";

# use class stringification overload to alternate
my $str2 = join( flipper->new(), %hash );
print "result: [$str2]\n";

#----------------------------------
package flipper;
use overload '""' => \&toString;
sub new {
  my $class = shift;
  my $self  = { counter => 0 };
  bless $self, $class;
}
sub toString {
  my $self = shift;
  return ( $self->{counter}++ % 2 ? '=' : ',' );
}