package SomeClass;

use strict;
use warnings;
use Class::Std;
{
    # Attributes
    my %whatever: ATTR;

    # this initializes the class in place of new
    sub BUILD {
        my ($self, $ident, $arg_ref) = @_;

        ...
        # Do some initialization stuff here
    }

    # here's a method that's private. It throws an exception when called from outside the class it's declared.
    sub some_method: PRIVATE {
        my ($self) = @_;

        ...
        # Some class stuff here
    }
}