I don't like that construction. If the "risky" methods are used in the parent class, the inheriting child class may die unexpectedly:

#!/usr/bin/perl -w
use strict;

package ParentClass;

sub new
{
    my $class=shift;
    return bless {},$class;
}

sub run
{
    my $self=shift;
    $self->hello();
    $self->risky();
    $self->world();
}

sub hello
{
    print "*** Hello ";
}

sub risky
{
    print "risky ";
}

sub world
{
    print "world! ***\n";
}

package ChildClass;

our @ISA=qw(ParentClass);

sub risky
{
    die "You're not allowed to call risky()";
}

package main;

$|=1;

print "ParentClass:\n";
my $p=ParentClass->new();
$p->run();
print "ChildClass:\n";
my $c=ChildClass->new();
$c->run();
[download]

The only clean solution is to have a common base class without the "risky" methods:

#!/usr/bin/perl -w
use strict;

package BaseClass;

sub new
{
    my $class=shift;
    return bless {},$class;
}

sub hello
{
    print "*** Hello ";
}

sub world
{
    print "world! ***\n";
}

package FormerParentClass;

our @ISA=qw(BaseClass);

sub risky
{
    print "risky ";
}

sub run
{
    my $self=shift;
    $self->hello();
    $self->risky();
    $self->world();
}

package FormerChildClass;

our @ISA=qw(BaseClass);

sub run
{
    my $self=shift;
    $self->hello();
    $self->world();
}

package main;

$|=1;

print "FormerParentClass:\n";
my $p=FormerParentClass->new();
$p->run();
print "FormerChildClass:\n";
my $c=FormerChildClass->new();
$c->run();
[download]

Alexander