filter: use metatables for filter definition interface

libs/filter.lua

@@ -1,29 +1,22 @@
 local txt = smart_inventory.txt
 local txt_usage = minetest.setting_get("smart_inventory_friendly_group_names") or false
 
-local filter = {}
-filter.registered_filter = {}
-
-function filter.get(name)
-	return filter.registered_filter[name]
+--------------------------------------------------------------
+-- Filter class
+--------------------------------------------------------------
+local filter_class = {}
+filter_class.__index = filter_class
+function filter_class:check_item_by_name(itemname)
+	if minetest.registered_items[itemname] then
+		return self.filter_func(minetest.registered_items[itemname])
+	end
 end
 
-function filter.register_filter(def)
-	assert(def.name, "filter needs a name")
-	assert(def.filter_func, "filter function required")
-	assert(not filter.registered_filter[def.name], "filter already exists")
-
-	local self = def
-
-	function self:check_item_by_name(itemname)
-		if minetest.registered_items[itemname] then
-			return self.filteget_group_descriptionr_func(minetest.registered_items[itemname])
-		end
-	end
-	function self:check_item_by_def(def)
+function filter_class:check_item_by_def(def)
 	return self.filter_func(def)
-	end
-	function self:get_description(group)
+end
+
+function filter_class:get_description(group)
 	local ret_desc
 	if self.shortdesc_func then
 		ret_desc = self:shortdesc_func(group)
@@ -39,9 +32,23 @@ function filter.register_filter(def)
 	else
 		return group.name
 	end
-	end
+end
 
-	filter.registered_filter[self.name] = self
+
+local filter = {}
+filter.registered_filter = {}
+
+function filter.get(name)
+	return filter.registered_filter[name]
+end
+
+function filter.register_filter(def)
+	assert(def.name, "filter needs a name")
+	assert(def.filter_func, "filter function required")
+	assert(not filter.registered_filter[def.name], "filter already exists")
+	setmetatable(def, filter_class)
+	def.__index = filter_class
+	filter.registered_filter[def.name] = def
 end
 
 filter.register_filter({