hump/class.lua

--[[
Copyright (c) 2010 Matthias Richter

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
]]--

local setmetatable, getmetatable = setmetatable, getmetatable
local type, assert, pairs = type, assert, pairs
local tostring, string_format = tostring, string.format
module(...)

local function __NULL__() end
function new(constructor)
	-- check name and constructor
	local name = '<unnamed class>'
	if type(constructor) == "table" then
		if constructor.name then name = constructor.name end
		constructor = constructor[1]
	end
	assert(not constructor or type(constructor) == "function",
		string_format('%s: constructor has to be nil or a function', name))

	-- build class
	local c = {}
	c.__index = c
	c.__tostring = function() return string_format("<instance of %s>", name) end
	c.construct = constructor or __NULL__
	c.Construct = constructor or __NULL__
	c.inherit = inherit
	c.Inherit = inherit

	local meta = {
		__call = function(self, ...)
			local obj = {}
			self.construct(obj, ...)
			return setmetatable(obj, self)
		end,
		__tostring = function() return tostring(name) end
	}

	return setmetatable(c, meta)
end

function inherit(class, interface, ...)
	if not interface then return end

	-- __index and construct are not overwritten as for them class[name] is defined
	for name, func in pairs(interface) do
		if not class[name] and type(func) == "function" then
			class[name] = func
		end
	end

	inherit(class, ...)
end

-- class() as shortcut to class.new()
do
	local m = {}
	m.__call = function(_, ...) return new(...) end
	setmetatable(_M, m)
end