sub f_windows {
}
sub f_linux  {
}
sub f_mac {
}

sub specific_f {
   my $dispatch_os = {
      "MSWin32" => \&f_windows,
      "linux"   => \&f_linux,
      "MacOS"   => \&f_mac
   };
   $dispatch_os->{$^O}->(@_);
}