Mastering Blockchain Programming with Solidity

Immutable code

Once you deploy your smart contract on Ethereum blockchain, either on the testnet or the mainnet, you cannot modify the code of the smart contract files that you have deployed. All code that is deployed becomes immutable. Not even an attacker/hacker can change the deployed code.

If your code is deployed on the testnet for testing purposes, then you can fix any issues in your smart contract files present on your local machine, and redeploy your code on the testnet again to check whether the functionality is working or not. But if you have deployed your contract on the mainnet (production) and other people, entities, or contracts started using that contract code, then you cannot change that contract code. If those entities are ...