This is very simple. Perl will automagically pass the object as the first argument to the subroutine if you use one of the method invocation syntaxes. When you say private method, what exactly do you mean btw? There is only one way that I know of to *enforce* private methods which is to make a lexical reference in the package to the subroutine. Once within a public method, the private method is visible and callable via method invocation. Back to your question. When calling a private method from a public method, just call like:

sub public_method {
   my $object = shift;
   $object->private_method;
}

sub private_method {
   my $object = shift;
   ...
}
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Basically, unless you create a lexical variable that contains a CODE ref, there is no way to really create and enforce a private method that I know of. This is by design BTW. Perl wisdom says that you shouldn't need a shotgun to keep people out of your living room. Thus your private methods are just conventions based on name normally. Like sub __private_method {}; rr