Advanced Perl Programming

Objects

Salient points:

• A class is a package. There’s no keyword such as struct or class to define layout of object.

• You choose object representation — object layout is not dictated by you.

• No special syntax for constructor. You choose the name of the subroutine that is going to allocate the object and return a blessed or typed reference to that object.

1. Creating an OO package — Method 1 (see also #19).

   The C++ class:

   class Employee {
       String _name; int _age; double _salary;
       Employee (String n, int age) : _name(n), _age(age), _salary(0) {}
       ~Employee {printf ("Ahh ... %s is dying\n", _name)}
       set_salary (double new_salary) { this->_salary = new_salary}
   };

   becomes:

   package Employee;
   sub create {                # Allocator and Initializer 
        my ($pkg, $name, $age) = @_;
        # Allocate anon hash, bless it, return it.
        return (bless {name => $name, age=> $age, salary=>0}, $pkg);
   }
   sub DESTROY {               # destructor (like Java's finalize)
       my $obj = shift;
       print "Ahh ... ", $obj->{name}, " is dying\n";
   }
   sub set_salary {
       my ($obj, $new_salary) = @_;
       $obj->{salary} = $new_salary; # Remember: $obj is ref-to-hash
       return $new_salary;
   }

2. Using object package:

   use Employee;
   $emp = Employee->create("Ada", 35);
   $emp->set_salary(1000);

3. Creating OO package — Method 2 (see also #17). Inherit from ObjectTemplate, use the attributes method to declare attribute names, and obtain the constructor new and attribute accessor functions for free:

   package Employee; use ObjectTemplate; @ISA = ("ObjectTemplate"); attributes("name", "age", "salary"); sub ...