Omitting Optional Arguments in Method Calls

When you call a vSphere API method by using vSphere SDK for Perl, and want to omit an optional argument, you can do one of two things.

• You can omit the argument.

  $vm->PowerOnVM(host => $host); # with the optional host argument
  $vm->PowerOnVM(); # without the optional host argument

• You can supply undef as the value of the optional argument.

  $vm->PowerOnVM(host => undef);

Supplying undef as the value of the optional argument is useful when the value of an argument, which might or might not be undef, is contained in a variable, as in the following example.

my $host = Vim::find_entity_view(
  view_type => 'HostSystem',
  filter => { name => 'preferredHost' }
);
$vm->PowerOnVM(host => $host);

You cannot use the empty string or the value 0 to represent undef or an unset parameter.