Introduce utility function for deriving table fields

tools/electric_chainsaw.lua

@@ -15,8 +15,7 @@
 -- along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 local S=minetest.get_translator("industrialtest")
-industrialtest.ElectricChainsawBase=table.copy(industrialtest.ActivatedElectricTool)
-industrialtest.internal.unpackTableInto(industrialtest.ElectricChainsawBase,{
+industrialtest.ElectricChainsawBase=industrialtest.internal.derive(industrialtest.ActivatedElectricTool,{
 	digs={"choppy"}
 })
 
@@ -33,8 +32,7 @@ function industrialtest.ElectricChainsawBase.getOpPower(self,itemstack)
 	return 50
 end
 
-industrialtest.ElectricChainsaw=table.copy(industrialtest.ElectricChainsawBase)
-industrialtest.internal.unpackTableInto(industrialtest.ElectricChainsaw,{
+industrialtest.ElectricChainsaw=industrialtest.internal.derive(industrialtest.ElectricChainsawBase,{
 	name="industrialtest:electric_chainsaw",
 	description=S("Electric Chainsaw"),
 	inventoryImage="industrialtest_electric_chainsaw.png",
@@ -61,8 +59,7 @@ minetest.register_craft({
 	}
 })
 
-industrialtest.AdvancedElectricChainsaw=table.copy(industrialtest.ElectricChainsawBase)
-industrialtest.internal.unpackTableInto(industrialtest.AdvancedElectricChainsaw,{
+industrialtest.AdvancedElectricChainsaw=industrialtest.internal.derive(industrialtest.ElectricChainsawBase,{
 	name="industrialtest:advanced_electric_chainsaw",
 	description=S("Advanced Electric Chainsaw"),
 	inventoryImage="industrialtest_advanced_electric_chainsaw.png",