ECS/class.lua

--[[
    Class system
    @author : Siapran Candoris
    Supports memoized multiple inheritance
]]--

local ipairs = ipairs

do
	local function metatable_search( k, list )
		for _,e in ipairs(list) do
			local v = e[k]
			if v then return v end
		end
	end

	local function metatable_cache( self, k )
		local v = metatable_search(k, self.__parents)
		self[k] = v
		return v
	end

	-- genealogy is
	local function make_genealogy( self, res, has )
		res = res or {}
		has = has or {}
		local parents = self.__parents
		if has[self] then
			return
		end
		if parents and #parents > 0 then
			for _,parent in ipairs(parents) do
				make_genealogy(parent, res, has)
			end
		end
		res[#res + 1] = self
		has[self] = true
		return res
	end

	-- make a class with simple or multiple inheritance
	-- inheritance is implemented as cached first found
	-- do NOT change class methods at runtime, just don't
	function make_class( ... )
		local res = {}
		res.__parents = {...}
		res.__genealogy = make_genealogy(res)
		res.__instanceof_cache = {}
		-- inherited methods are cached to improve runtime performance
		-- caching is done per class, not per object
		if #res.__parents > 0 then
			setmetatable(res, {__index = metatable_cache})
		end

		res.__index = res

		return res
	end
end

return make_class