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.
-
Creating an OO package - Method 1 (see also #
19
).
The C++ class:
class Employee {
String _name; int _age; double _salary;
create (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;
}
-
Using object package:
use Employee;
$emp = Employee->new("Ada", 35);
$emp->set_salary(1000);
-
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 DESTROY {
my $obj = shift;
print "Ahh ... ", $obj->name(), " is dying\n";
}
sub set_salary {
my ($obj, $new_salary) = @_;
$obj->salary($new_salary);
}
-
Class methods:
Employee->print(); # 1. "Arrow notation" used for class method
new Employee (); # 2. Class method using "Indirect notation".
These two class methods must expect the package name as the first parameter, followed by the rest of the arguments.
-
Instance methods. There are two ways of invoking methods on an object:
$emp->promote();
promote $obj;
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