/zoeplat

-- Class: Class

-- This is a simple OOP single-inheritance implementation based

-- on the one suggested by <Programming in Lua at http://www.lua.org/pil/16.html>.

-- One big difference from what you may be expecting is that there are no

-- constructors per se; all subclasses share the same constructor method,

-- which takes a table of properties that are mixed into the instance.

-- e.g. Code like this:

--

-- (begin code)

-- MyClass = Class:extend{ color = 'red', name = 'robin' }

-- myObject = MyClass:new{ color = 'blue' }

-- (end code)

--

-- Would set myObject to have a color of 'blue' and a name of 'robin'. There is a

-- <onNew> event handler you can use to perform initialization based on these values.

--

-- Event: onNew

-- 		Called once, when a new object is created via <new()>.

Class = {

	-- Method: extend

	-- Creates a subclass of a class object, replacing any class properties

	-- with those in the object passed. It also sets the subclass's prototype

	-- property to this class. This alters the passed table in-place.

	--

	-- Arguments:

	-- 		obj - table of properties

	--

	-- Returns:

	-- 		subclassed table

	extend = function (self, obj)

		obj = obj or {}

		assert(type(obj) == 'table', 'must extend a table, received a ' .. type(obj))

		-- copy any table properties into the subclass, so that

		-- it does not accidentally overwrite them

		for key, value in pairs(self) do

			if key ~= '__index' and not obj[key] and type(value) == 'table' then

				obj[key] = copyTable(self[key])

			end

		end

		-- __index work to set up inheritance and getters/setters

		obj = obj or {}

		setmetatable(obj, self)

		self.__index = self

		obj.prototype = self

		return obj

	end,

	-- Method: new

	-- Extends an object and calls its onNew() handler if it is defined.

	-- This handler is meant for object-specific initialization,

	-- not class-wide work.

	--

	-- Arguments:

	--		obj - table of properties that the new object starts with,

	--			  overriding anything set in the class

	-- 

	-- Returns:

	-- 		new instance

	new = function (self, obj)

		obj = self:extend(obj)

		if obj.onNew then obj:onNew() end

		return obj

	end,

	-- Method: mixin

	-- Mixes all properties passed into the current object, overwriting any

	-- pre-existing values.

	--

	-- Arguments:

	--		obj - table of properties to mix into the object

	--

	-- Returns:

	--		current object

	mixin = function (self, obj)

		assert(type(obj) == 'table', 'must mix in a table, received a ' .. type(obj))

		for key, value in pairs(obj) do

			self[key] = obj[key]

		end

	end,

	-- Function: instanceOf

	-- Checks whether a certain object is anywhere in its inheritance chain.

	--

	-- Arguments:

	-- 		class - table to check against

	--

	-- Returns:

	-- 		boolean

	instanceOf = function (self, class)

		local proto = self.prototype

		while proto do

			if proto == class then

				return true

			end

			proto = proto.prototype

		end

		return false

	end

}