Object Oriented Programming

wiki

Learning Material

• ObjectOrientationTutorial - tutorial on OOP with classes.
• InheritanceTutorial - tutorial on OOP using inheritance[2] with classes and prototypes.
• [Chapter on OOP] from [PiL] - a comprehensive view of OOP in Lua by the language's chief-architect.
• ObjectOrientationClosureApproach - alternative approach to OOP.

Related Discussions

• ColonForMethodCall - discussion about the use of colon (:) instead of period (.) for methods calls.
• ObjectBenchmarkTests - performance evaluation of different approaches to access objects members.

Feature Implementations

• SimpleLuaClasses - classes with constructors.
• LuaClassesWithMetatable - classes with constructor and copy operations.
• ClassesAndMethodsExample - classes with constructors and simple inheritance.
• ObjectProperties - getters/setters that look like table field accesses (like properties in C#).
• ProxyBasedEncapsulation - encapsulation of objects via proxy tables.
• ClassesAsConstructorClosures - a flexible way of implementing classes with type testing.

Older Lua Versions

• ClassesAndMethods - classes using tagmethods of Lua 4.0.
• ClassesAndMethodsWithEventtable - classes using metatables of a pre-release version of Lua 5.0.

Feature Modules

• [lclass] - Barebones Lua with Classes (73 SLOC), inspired by Lua's lightweight design, features:
  • constructor/initialization
  • simple inheritance
• YetAnotherClassImplementation - support for classes with:
  • constructor/initialization
  • simple inheritance
  • virtual methods
  • access control to inherited attributes
  • type casting
• MultipleInheritanceClasses - support for classes with:
  • constructor/initialization
  • multiple inheritance
  • shared derivation (like C++ virtual)
  • handling of ambiguities and inherited attributes
• ObjectLua - support for object prototyping and classes with:
  • constructor/initialization
  • simple inheritance
  • mandatory root class Object
  • access to the originally inherited implementation in overridden methods through function super, similarly to Java and Python classes
• KlassModule - support for classes with:
  • constructors and destructors
  • simple prototype-based inheritance
  • isA method
  • works with Lua 5.2
• [LOOP] - light-weight modules that incrementally support:
  • loop.base classes with constructor/initialization support
  • loop.simple classes with simple inheritance
  • loop.multiple classes with multiple inheritance
  • loop.cached classes with inheritance that copies members from superclasses (faster method resolution and inheritance of metamethods)
  • loop.scoped classes with private and protected access to members
• [lua-Coat] - port of [Coat] (a light-weight OO model of Perl5) that supports:
  • constructor/initialization
  • multiple inheritance
  • method modifiers
  • introspection operations
  • attribute checking
  • additional support for roles and type declarations
• [MiddleClass] - single file module (~100 LoC) that supports classes with:
  • constructor/initialization
  • simple inheritance
  • mandatory root class Object
  • basic mixins support (copying methods)
  • getter/setter construction facilities
  • additional lib [MiddleClass-extras] with mixins that improve upon the basic functionality.
• [OWL] - single file module that provides a class implementation with the following features:
  • constructor/initialization (can also be overridden on a per-instance basis).
  • multi-level inheritance (all the way to top-level super class).
  • easy-to-use with two primary functions: class() and instance()
  • common OOP methods: is_a(), kind_of(), and instance_of().
  • private class table (inherited by sub-classes, but not by instance objects).
  • easily implement basic metamethods via add_property_callback() method.
  • several samples and documentation included
  • compatible with Corona SDK (provides display object classes), as well as non-Corona projects.
• [30log] - single file module. It features:
  • named and unnamed classes
  • constructor/initialization
  • default values for properties
  • single inheritance
  • basic support for mixins
• [lupy] - single file module(~50 sloc, ~2 kb). It's a Python-style class implementation with several Ruby features:
  • constructor/initialization
  • single inheritance
  • basic mixins support
  • missing methods handler
  • monkey patching support
  • lexical scope based encapsulation
  • inheritance tree based type testing
  • namespace and inner class support
• [classy] - single file module (~460 sloc, ~14 kb) with:
  • constructor/initialization (efficient, necessary data precomputed during class definition)
  • multiple inheritance (method lookups in width-first search order)
  • efficient method calls (method lookup precomputed during class definition)
  • monkey patching support (updates to base classes propagate to derived classes)
  • multi methods (functions with more than one polymorphic parameter)
• [lua-objects] - single file module (~300 sloc) with:
  • new! customizable methods and names for constructor/destructor
  • new! multiple inheritance (all way to top level)
  • new! handles ambiguities of inherited attributes
  • new! advanced support for mixins
  • new! default inherited class, Class
  • getters and setters
  • correctly handles missing methods on super classes – superCall()
  • optimization (methods from super classes can be cached on class/instance)
  • common methods/properties – .is_class, .is_instance, .isa(), .supers. .class

  [dmc-objects] is collection of lua-object sub-classes made for the Corona SDK. they show examples of:

  • custom constructor/intialization/destructor
  • custom constructor/destructor names
  • mixin usage, Event mixin ([lua-events-mixin]) for event capabilities (add/removeEventListener, etc)
  • dmc-objects classes, several Corona apps using dmc-objects
• [PLoop] - a powerful C# Style OOP System (~12391 sloc, ~639 kb) with:
  • a full set OOP system that provide prototype, attribute, environment, enum, struct, interface, class and more.
  • full and customizable type validation, function argument validation, method overloads and etc.
  • thread pool, collection, serialization and other features for common usage.
• [SIMPLOO] - Simple Lua Object Orientation (~500 sloc, ~10 kb minified):
  • Use a simple syntax similar to other object-oriented languages, or use traditional lua tables.
  • Define constructors and finalizers. Finalizers are called on garbage collection (also works in Lua 5.1 using newproxy).
  • Keywords such as as private, public, abstract, static, const and meta (to define in-class metamethods).
  • Multiple inheritance. Warns on ambiguous naming. Parent members are stored as direct references in children to keep things fast.
  • Define class namespaces using a dot separated class name. Import classes from other namespaces. Define aliases for your imported classes. Uses function environments.
  • A production mode config setting is included to speed up the library even more by disabling non-critical pieces of code.
  • Class data is precomputed during definition. Instantiation times are O(n) where n = number of class member, due to a simple deep copy of this data.
  • Namespaces are stored as nested global tables for easy access. Classes have common helper methods such as: get_name(), get_class(), instance_of().
• [oop.lua] - a support library for prototype-based programming in Lua.
• [Luaoop] - single file module, simple class-based OOP library
  • multiple inheritance
  • reflection
  • operators
  • destructor
  • behavior transfer
• [POOL] - Poorman's Object-Oriented Lua
  • single file module
  • class template table
  • constructor/destructor
  • inheritance/polymorphism
  • operators

Sample Implementations

• PointAndComplex - classes for points and complex numbers (uses SimpleLuaClasses).
• [LOOP Library] - class library with various OO implementations (uses [LOOP] modules):
  • data strucutures (ex. memoization cache).
  • debugging utilities (ex. pretty-priting, logging).
  • serialization utilities (ex. streams).
  • coroutine-based multithreading utilities (ex. timers, cooperative sockets, etc.).
  • and other OO utilities (ex.: wrappers, publishers).

See Also

• SampleCode