NAME

Object::Pad - a simple syntax for lexical slot-based objects

SYNOPSIS

use Object::Pad;

class Point {
   has $x;
   has $y;

   method CREATE {
      $x = $y = 0;
   }

   method move {
      $x += shift;
      $y += shift;
   }

   method describe {
      print "A point at ($x, $y)\n";
   }
}

DESCRIPTION

WARNING This is a highly experimental proof-of-concept. Please don't actually use this in production :)

This module provides a simple syntax for creating object classes, which uses private variables that look like lexicals as object member attributes.

KEYWORDS

class

class Name {
   ...
}

Behaves similarly to the package keyword, but provides a package that defines a new class. Such a class provides an automatic constructor method called new, which will invoke the class's CREATE method if it exists.

has

has $var;
has @var;
has %var;

Declares that the instances of the class have a member attribute of the given name. This member attribute (called a "slot") will be accessible as a lexical variable within any method declarations in the class.

Array and hash members are permitted and behave as expected; you do not need to store references to anonymous arrays or hashes.

method

method NAME {
   ...
}

method NAME (SIGNATURE) {
   ...
}

method NAME :attrs... {
   ...
}

Declares a new named method. This behaves similarly to the sub keyword, except that within the body of the method all of the member attributes ("slots") are also accessible. In addition, the method body will have a lexical called $self which contains the invocant object directly; it will already have been shifted from the @_ array.

The signatures feature is automatically enabled for method declarations.

A list of attributes may be supplied as for sub. The most useful of these is :lvalue, allowing easy creation of read-write accessors for slots.

class Counter {
   has $count;

   method count :lvalue { $count }
}

my $c = Counter->new;
$c->count++;

IMPLIED PRAGMATA

In order to encourage users to write clean, modern code, the body of the class block acts as if the following pragmata are in effect:

use strict;
use warnings;
no indirect ':fatal';
use feature 'signatures';

TODO

• Setting default package using class Name; statement without block.

• Subclassing. Single-inheritence is easier than multi so maybe that first.

• Detect and croak on attempts to invoke method subs on non-instances.

• Experiment with CvOUTSIDE or other techniques as a way to set up the per-method pad, and consider if we can detect which slots are in use that way to improve method-enter performance.

• Some extensions of the has syntax:

  Default expressions

  has $var = DEFAULT;

  A way to request generated accessors - ro or rw.

AUTHOR

Paul Evans <leonerd@leonerd.org.uk>