Require vs Revert – When to Use Require vs Custom Revert Errors in Smart Contracts

custom-errorsrequirerevert-opcode

This applies only to solidity ^0.8 and onward.

Let's say I have a function like this:

function withdraw() external {
  (bool success, ) = payable(msg.sender).call{value: address(this).balance}("");
  // Now we should check the function succeeded
}

I could check this with:

require(success, "Transfer failed");

// At the top of the code
error TransferFailed();
.
.
.
if(!success){ revert TransferFailed();}

Where does it make sense to use require vs a custom error and revert? It seems you'll just need to check the gas costs, and that's it.

Best Answer

Custom errors are more gas efficient than using require with a string explanation. So ideally you'd always use this over require.

Related Solutions

Solidity: Custom Error Message in require() Not Showing

You can't currently use web3 to inspect error messages thrown from revert. In the future it may be possible though, so adding these to your smart contract helps to future proof against this development.

You can follow the discussion at:
https://github.com/ethereum/EIPs/pull/658

Solidity – How to Bubble Up a Custom Error When Using DELEGATECALL in Solidity

Check out this function I modified from the openzepplin's Address.sol.

function _delegatecall(address target, bytes memory data) internal returns (bytes memory) {
    (bool success, bytes memory returndata) = target.delegatecall(data);
    if (!success) {
        if (returndata.length == 0) revert();
        assembly {
            revert(add(32, returndata), mload(returndata))
        }
    }
    return returndata;
}

returndata is a dynamic-sized byte array. If the delegate call fails, returndata would be the error object raised by the failed call. Say I have contract A which delegate calls to contract B. The latter reverts with the custom error GonnaMakeIt(uint256 data). Then, the returndata would be:

0xbf42f2660000000000000000000000000000000000000000000000000000000000000539
  +------+---------------------------------------------------------------+
  selector                       uint256 data

Then, we make use of Yul's revert(p, s) to revert with the custom error in contract A. p refers to the pointer of where the error byte array starts, s refers to the how long the byte array is.

Since returndata is a dynamic-sized byte array, the first 32 bit of the pointer stores the size of it, which we mload(returndata) to retrieve it. And similarly, add(32, returndata) would be the pointer to where the byte array starts. Altogther, it forms the line revert(add(32, returndata), mload(returndata)), which reverts the error you get from contract B.

Best Answer

Related Solutions

Solidity: Custom Error Message in require() Not Showing

Solidity – How to Bubble Up a Custom Error When Using DELEGATECALL in Solidity

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