Blessed References

Perl object system

Perl’s core object system is deliberately minimal. It has only three rules:

• A class is a package.

• A method is a function.

• A (blessed) reference is an object.

We can build anything else out of these three rules. This minimalism can be impractical for larger projects, in particular, the possibilities for greater abstraction through metaprogrammingWriting programs to write programs for you—metaprogramming or code generation—allows you to build reusable abstractions. are awkward and limited. Moose is a better choice for modern programs larger than a couple hundred lines, although plenty of legacy code uses Perl’s default OO.

The bless built-in

We’ve seen the first two rules already. The bless built-in associates the name of a class with a reference. That reference is now a valid invocant. Perl will perform method dispatch on it. A constructor is a method that creates and blesses a reference. By convention, they are named new(). Constructors are also almost always class methods.

bless takes two operands, a reference and a class name, and evaluates to the reference. The reference may be any valid reference, empty or not. The class doesn't have to exist yet. We may even use bless outside a constructor or a class, but we’d be violating encapsulation to expose the details of object construction outside a constructor. A constructor can be as simple as this: