Add an allow_shot field to throwing.register_bow definition table

And make the throwing.throw_arrow function able to throw any item

README.md

@@ -36,6 +36,11 @@ Definition: definition table, containing:
   * description (highly recommended): description of the bow.
   * texture (essential): texture of the bow, shown in inventory.
   * groups (optional): groups of the item.
+  * allow_shot (optional): function(player, itemstack):
+    - player: the player using the bow
+    - itemstack: the itemstack of the bow
+    - should return true if the shot can be made, and false otherwise
+    - default for this is function(player, itemstack) return throwing.is_arrow(itemstack) end
 ]]
 
 -- Example:

init.lua

@@ -9,13 +9,27 @@ throwing.target_both = 3
 throwing.modname = minetest.get_current_modname()
 
 --------- Arrows functions ---------
+function throwing.is_arrow(itemstack)
+	for _, arrow in ipairs(throwing.arrows) do
+		if (type(itemstack) == "string" and itemstack or itemstack:get_name()) == arrow then
+			return true
+		end
+	end
+	return false
+end
+
 local function shoot_arrow(itemstack, player)
 	local inventory = player:get_inventory()
-	for _,arrow in ipairs(throwing.arrows) do
-		if inventory:get_stack("main", player:get_wield_index()+1):get_name() == arrow then
+	local arrow = inventory:get_stack("main", player:get_wield_index()+1):get_name()
+
 	local playerpos = player:getpos()
 	local pos = {x=playerpos.x,y=playerpos.y+1.5,z=playerpos.z}
-			local obj = minetest.add_entity(pos, arrow.."_entity")
+	local obj
+	if throwing.is_arrow(arrow) then
+		obj = minetest.add_entity(pos, arrow.."_entity")
+	else
+		obj = minetest.add_entity(pos, "__builtin:item", arrow)
+	end
 
 	local luaentity = obj:get_luaentity()
 	luaentity.player = player:get_player_name()
@@ -41,13 +55,10 @@ local function shoot_arrow(itemstack, player)
 	end
 
 	if not minetest.setting_getbool("creative_mode") then
-				inventory:remove_item("main", arrow)
+		player:get_inventory():remove_item("main", arrow)
 	end
 
 	return true
-		end
-	end
-	return false
 end
 
 local function arrow_step(self, dtime)
@@ -269,10 +280,18 @@ end
 
 ---------- Bows -----------
 function throwing.register_bow(name, def)
+	if not def.allow_shot then
+		def.allow_shot = function(player, itemstack)
+			return throwing.is_arrow(itemstack)
+		end
+	end
 	minetest.register_tool(throwing.modname..":"..name, {
 		description = def.description,
 		inventory_image = def.texture,
 		on_use = function(itemstack, user, pointed_thing)
+			if not def.allow_shot(user, user:get_inventory():get_stack("main", user:get_wield_index()+1)) then
+				return itemstack
+			end
 			if shoot_arrow(itemstack, user, pointed_thing) then
 				if not minetest.setting_getbool("creative_mode") then
 					itemstack:add_wear(65535/30)