Introduce utility function for deriving table fields

tools/jetpack.lua

@@ -15,8 +15,7 @@
 -- along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 local S=minetest.get_translator("industrialtest")
-industrialtest.JetpackBase=table.copy(industrialtest.GearTool)
-industrialtest.internal.unpackTableInto(industrialtest.JetpackBase,{
+industrialtest.JetpackBase=industrialtest.internal.derive(industrialtest.GearTool,{
 	part="torso"
 })
 local soundHandles = {}
@@ -47,8 +46,7 @@ function industrialtest.JetpackBase.update(self, player, inv, itemstack, dtime)
 	return false
 end
 
-industrialtest.Jetpack=table.copy(industrialtest.JetpackBase)
-industrialtest.internal.unpackTableInto(industrialtest.Jetpack,{
+industrialtest.Jetpack=industrialtest.internal.derive(industrialtest.JetpackBase,{
 	-- _v is hack to suppress "Registered armor doesn't have material at the end of registration name" warning from 3D Armor.
 	name="industrialtest:jetpack_v",
 	description=S("Jetpack"),
@@ -84,8 +82,7 @@ minetest.register_craft({
 	}
 })
 
-industrialtest.ElectricJetpack=table.copy(industrialtest.JetpackBase)
-industrialtest.internal.unpackTableInto(industrialtest.ElectricJetpack,{
+industrialtest.ElectricJetpack=industrialtest.internal.derive(industrialtest.JetpackBase,{
 	name="industrialtest:electric_jetpack",
 	description=S("Electric Jetpack"),
 	inventoryImage="industrialtest_electric_jetpack_inv.png",