0

I'm an absolute beginner with Solidity so apologies if this is a noob question. I'm building projects to learn solidity, and I currently want to build a smart contract which I can kill if I need to.

I found the selfdestruct() function but I'm a bit confused about how it works. Once my smart contract is deployed, how can I activate the selfdestruct() function when I want to?

Any guidance appreciated - including links for further reading/study.

Thanks in advance.

1 Answer 1

0

The following contract shows how to use selfdestruct, in this example the usage is restricted to the owner of the smart contract :

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract Destruct {

    address owner;

    modifier onlyOwner() {
        require(msg.sender == owner, "Not the owner");
        _;
    }

    constructor() {
        owner = msg.sender;
    }

    function callSelfDestruct() onlyOwner public {
        selfdestruct(payable(owner));
    }
}

I'm building projects to learn solidity, and I currently want to build a smart contract which I can kill if I need to.

While maintaining a clean state is a good thing (i.e., selfdestruct the contracts that won't see any more usage to free some space on the global state) you should also be aware that this will most definitely be seen as a security risk by potential users.

I found the selfdestruct() function but I'm a bit confused about how it works

selfdestruct is very particular in the blockchain space, basically when called it will forward all the contract balance to the target address specified in its arguments (owner in the example above). This balance forwarding will bypass every check, will not trigger any receive() or fallback(). So no matter what type of account is behind the target address, its balance will be increased by the self-destructing contract's balance.

When the tx is committed to the state (that is after its execution is finished) the contract's code will be removed from the global state, it's not disabled, it's deleted.

how can I activate the selfdestruct() function when I want to?

You must include the call in your contract's code, as in the example above.

Following this example, whenever the owner wants to selfdestruct the contract, it must call the callSelfDestruct function.


On a side note, you should be aware that there are ongoing effort to remove / disable the selfdestruct behavior, do not rely on it working in the future.

I hope that answers your question.

3
  • This is incredibly helpful and educational, thank you! I didn't realise the security risks and that the function might be discontinued in the future. I have a follow-up question, if you don't mind: "Following this example, whenever the owner wants to selfdestruct the contract, it must call the callSelfDestruct function." What I don't understand is how I can call the callSelfDestruct function if my smart contract is already deployed? Do I make a new smart contract to do it?
    – mess1n
    Mar 24, 2022 at 10:21
  • When I say 'call' here, I mean make a public transaction calling the callSelfDestruct function, you can do that from Remix, web3 or ethers as you want. You can also use another contract between you and the contract to self destruct yes, but you'll still need to initiate the call chain with a public transaction triggering your intermediate contract.
    – hroussille
    Mar 24, 2022 at 11:10
  • Ah! OK, I think I follow - at least that's enough for me to look into it more myself. Thanks so much for your help.
    – mess1n
    Mar 24, 2022 at 13:22

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.