FYI, here is my test on whether the => operator stringifies its left operand, if the lop is an object:

my $obj = Stringy->new( 'the look' );

my $counter = 0;
for my $it ( a1 => $obj => 2 => 3 => 4, 5 ) {
  $counter++;
  print "iteration: $counter ";
  print "with (" . $it . ")";
  print "\n";
}

#-------------------------------------------------------
package Stringy;
use strict;
use overload (
    '""' => \&toString,
  );
1;
sub new {
  my $class = shift;
  my $self = { appearance => shift, };
  return bless $self, $class;
}
sub toString {
  my $self = shift;
  print "[toString called] ";
  return $self->{appearance};
}
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Run this, and you'll note that the object is stringified during the print as expected.

Comment out the 'print "with...' line, and you will note that the object is never stringified, not even by the => operator in the for (...) list.