Self Destruct

In Solidity, the selfdestruct function is used to destroy a contract and send its remaining ether balance to a designated address.

The syntax for selfdestruct is as follows:

scssCopy codeselfdestruct(address payable recipient);

The recipient parameter is the address where the remaining ether balance of the contract will be sent after the contract is destroyed. The recipient parameter must be a payable address, meaning it has a payable modifier and can receive ether.

It is important to note that once a contract is destroyed using selfdestruct, it cannot be recovered and any remaining data on the contract is permanently lost. Therefore, selfdestruct should only be used when it is necessary and appropriate.

When a contract is self-destructed using the selfdestruct function, the code of the contract is removed from the blockchain, but the state variables and the balance of the contract are not deleted. Instead, the remaining ether in the contract is sent to the designated recipient address specified in the argument of the selfdestruct function. The state variables of the contract will still be present on the blockchain, but they will no longer be accessible through the destroyed contract's address.

Instead of self-destructing the contract, you could disable its functionality by setting state variables so that nobody can call the function or send ether in the future. This can be done by adding a bool variable that is set to false when the contract is no longer needed. Then, in each function, you can add a require statement that checks if this variable is true. If it's false, the function will revert the transaction and prevent any further actions on the contract. This approach is safer because it doesn't delete the contract and all of its state and history from the blockchain, but rather simply makes it non-functional.

Even if a contract is removed by selfdestruct, it is still part of the history of the blockchain and probably retained by most Ethereum nodes. So using selfdestruct is not the same as deleting data from a hard disk.

Introduction to Smart Contracts — Solidity 0.8.19 documentation