IU

IU is a simple Object-Oriented model for Lua scripting. It simplifies the process of writing Lua scripts by allowing the use of standard OO paradigms. This library is designed to be very small; I've worked hard to make sure it remains under ~50 lines so that it is not a big dependency. Also, this model is not comprehensive, but handles most general cases.

Features

• Classes can inherit from one other class
• Classes can be constructed from base tables via the new operator
• Superclass functions are available via self:spr(<name>,...)
• Sane defaults for unimplemented classes are provided
• All object instances get a unique identifier available using self._id or <inst>._id
• A meaningful "toString" method is provided, so print(<inst>) and print(<class>) actually do something useful

Special Functions

IU provides a set of special functions for utilizing its OO model, as well as the nested table structure:

• def(<name>,[root]): The entry point into the IU class system. Declares a class object with the given name and parent/base class. The root parameter is optional; unspecified, the class inherits from the root Object class.

    A = cls.def('A')    -- Class A
    B = cls.def('B', A) -- Class B, inherits A
  

• self:spr(<name>,...): Super method helper function. Accesses the superclass table with the given function name, and attempts to call it with the specified arguments.

• self:udc(<name>,...): Userdata helper function. Accesses methods on the embedded user data, passing a reference to the Userdata object instead of a reference to self. This is provided for libraries like Love2d (see below), which use functions that produce Userdata objects when called. The IU class model allows for IU classes to be based on Userdata objects by defining a new function on the class.

Other Helpful Functions

• slice(array,start,[end]): Produces an array segment from start to end. The end parameter is optional; if unspecified, it will slice up to the end of the array. Negative end slices can be specified, which slices up to the -nth index counting from the right end.

    local a = {1, 2, 3, 4, 5}
    slice(a,2)    => {2,3,4,5}
    slice(a,1,3)  => {1,2,3}
    slice(a,1,-1) => {1,2,3,4,5}
  

• isCls(o): Checks if the given object is a IU class. This function is guarded, so any Lua type can be checked without causing an Error. This function returns false instead of nil when the object is NOT a class.

• isIns(o): Checks if the given object is an instance of a IU class. This function is guarded, so any Lua type can be checked without causing an Error. This function returns false instead of nil when the object is not a IU instance.

Examples

See the test_suite.lua file for a comprehensive example of all of the features that this OO model supports. Additional examples are listed below:

Base Table Construction

IU integrates well with other class / table systems, allowing you to construct IU classes that are based on non-empty tables. This allows direct integration with frameworks like Love2d and CoronaSDK, which use their own object models for objects. An example for Love2d is below:

cls = require('iu')

Body = cls.def('Body')
function Body:new(...)
    return love.physics.newBody(unpack(cls.slice(arg,1,5))), cls.slice(arg,6)
end

function love.load()
    local w = love.physics.newWorld(0,0,650,650)
    w:setGravity(0,700)
    w:setMeter(64)

    local ground = Body(w, 650/2, 625, 0, 0)
    print('Body at: ['..ground:udc('getX')..', '..ground:udc('getY')..']')
end

Inheritance

cls = require('iu')
  
A = cls.def('A')
function A:init()
    self.a = 10
end
B = cls.def('B', A)
function B:init()
    self:spr('init')
    self.b = 20
end
local b = B()
print('B a: '..b.a..' b: '..b.b)

Operator Overloading

cls = require('iu')

A = cls.def('A')
function A:init(n)
    self.n = n
end
function A:str()
    return self._id..': '..self.n
end
function A:add(o)
    return A(self.n+o.n)
end

local a1 = A(2)
local a2 = A(2)
local a3 = a1 + a2
print(a1, a2, a3)

TODO

• Fix the get and set methods in the base class. The IU core object has been written to support overloading these functions so you can manipulate index read and write. Right now, the functionality is there but it chains infinitely due to the way the code is structured. In the future, I might fix this; right now I think that its best to keep it simple.
• Explore other means of handling Userdata objects. The udc method isn't bad, but its not as streamlined as I would have liked it to be. The problem is that lua doesn't have an easy way to manipulate the behavior of calling functions via the colon syntax. Self is always passed, where we actually need a reference to the Userdata object (at least in the case of Love2d).

NAME

IU is named after the Lojban attitudinal (basically, a verbal version of this emoticon: <3) by the same name, meaning the emotion of *love*. This library was originally written for the purpose of utilizing it with Love2d, which is an awesome game framework :)