Token Ejector

If you are developing a smart contract that plans to hold Ditto clones, it is worth considering implementing the token ejector.

interface IERC721TokenEjector {

    function onERC721Ejected(
        address operator,
        address to,
        uint256 id,
        bytes calldata data
    ) external returns (bytes4);

}

Because a clone can be force transferred to a new owner via the Ditto auction mechanism, the Ditto contract will try to call the onERC721Ejected function on the previous owner.

if (from.code.length != 0) {
    try IERC721TokenEjector(from).onERC721Ejected{gas: 30000}(address(this), to, id, "") {}
    catch {}
}

This will allow any smart contract that implements the token ejector a chance to do their own accounting or enact any necessary actions when the clone is force transferred from them.

The function call is given up to a 30_000 gas stipend to accomplish its goals. This should be more than enough gas to get anything reasonable done.

If your contract does not implement onERC721Ejected the forced transfer will proceed as intended in any case.

It is highly recommended when implementing onERC721Ejected to check that msg.sender and/or operator are coming from the expected address. Not properly checking these could result in a potential exploit or unintended behaviour.