proper metatables usage

libs/crecipes.lua

@@ -9,7 +9,7 @@ crecipes.crecipes = {} --list of all recipes
 -- crecipe: Class
 -----------------------------------------------------
 local crecipe_class = {}
-crecipe_class.__index = crecipe_class
+local crecipe_class_mt = {__index = crecipe_class}
 crecipes.crecipe_class = crecipe_class
 
 -----------------------------------------------------
@@ -285,14 +285,12 @@ end
 -- Recipe object Constructor
 -----------------------------------------------------
 function crecipes.new(recipe)
-	local def = {}
-	def.out_item = nil
-	def._recipe = recipe
-	def.recipe_type = recipe.type
-	def._items = {}
-	setmetatable(def, crecipe_class)
-	def.__index = crecipe_class
-	return def
+	local self = setmetatable({}, crecipe_class_mt)
+	-- self.out_item = nil
+	self._recipe = recipe
+	self.recipe_type = recipe.type
+	self._items = {}
+	return self
 end
 
 -----------------------------------------------------

libs/filter.lua

@@ -4,7 +4,7 @@ local txt = smart_inventory.txt
 -- Filter class
 --------------------------------------------------------------
 local filter_class = {}
-filter_class.__index = filter_class
+local filter_class_mt = {__index = filter_class}
 
 function filter_class:check_item_by_name(itemname)
 	if minetest.registered_items[itemname] then
@@ -52,8 +52,7 @@ function filter.register_filter(def)
 	assert(def.name, "filter needs a name")
 	assert(def.check_item_by_def, "filter function check_item_by_def required")
 	assert(not filter.registered_filter[def.name], "filter already exists")
-	setmetatable(def, filter_class)
-	def.__index = filter_class
+	setmetatable(def, filter_class_mt)
 	filter.registered_filter[def.name] = def
 end
 

libs/maininv.lua

@@ -1,6 +1,6 @@
 -- Enhanced main inventory methods
 local maininvClass = {}
-maininvClass.__index = maininvClass
+maininvClass_mt = {__index = maininvClass}
 
 -- Clear the inventory
 function maininvClass:remove_all()
@@ -144,7 +144,7 @@ end
 -- player inventory class
 local maininv = {}
 function maininv.get(playername)
-	local self = setmetatable({}, maininvClass)
+	local self = setmetatable({}, maininvClass_mt)
 	self.playername = playername
 	self.inventory = minetest.get_player_by_name(playername):get_inventory()
 	self.inventory:set_width("craft", 3)