I think it looks better if one makes use of $a and $b

sub map2(&@) {
  my $f = shift;
  my @res;

  no strict 'refs';
  my $caller = caller;
  local(*{$caller."::a"}) = \my $a;
  local(*{$caller."::b"}) = \my $b;

  if (defined(wantarray)) {
    push @res, $f->($a,$b) while ($a, $b) = splice @_, 0, 2;
    return @res;
  } else {
    $f->($a,$b)            while ($a, $b) = splice @_, 0, 2;
  }
}


# ...
%h_prefixed = map2 { ($a, "p$b") } %h;
@a_hashed = map2 { +{ $a => $b } } @a;
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