Question

I have a subclass that calls a method from a superclass. The method in the superclass uses a method that is defined in the superclass as abstract (not really abstract) but implemented in the subclass.

For example:

package BaseClass;

sub new
{

}
sub method1 {

    return someAbstractMethod();
}



sub someAbtsractMethod
{
     die "oops, this is an abstract method that should " . 
         "be implemented in a subclass" ;
}
1;

package SubClass;

sub new
{

}

sub someAbtsractMethod
{
     print "now we implement the asbtract method";
}
1;

Now when I do:

$sub = new SubClass();
$sub->method1();

…it calls the abstract message and I get the specified error message. If I took off the abstract method from the super class and just leave the implementation in the subclass, It does not recognize the method and I get subroutine abstract method not found error.

Answer 1

There are some problems with your code, you need to tell the subclass what its parent class is. You also probably need to setup your constructors to pass through to the parent class. There were also a few misspellings in there.

package BaseClass;

sub new {
    bless {} => shift;
}
sub method1 {
    my $self = shift;

    return $self->someAbstractMethod();
}


sub someAbstractMethod
{
     die "oops, this is an abstract method that should " . 
         "be implemented in a subclass";
}


package SubClass;
use base 'BaseClass';

sub new {
    shift->SUPER::new
}

sub someAbstractMethod
{
     print "now we implement the asbtract method\n";
}


package main;

my $obj = BaseClass->new;

eval {$obj->method1(); 1} or warn $@;

my $subobj = SubClass->new;

$subobj->method1();