Enhancement lib Indexed to contain `LASTSEEN_BLOCKNUMBER`

[MASDXI]

Problem

The deployed block concept is simple and good, but it can be better. cause some L2 not using block.number for return current block height. and to not always use lastest block number when filter log can use LASTSEEN_BLOCKNUMBER which is lastest action of contract and open design of choice, e.g,, every 10,000 blocks, then stamp LASTSEEN_BLOCKNUMBER

Solution

Reference Implementation

// SPDX-License-Identifier: Apache-2.0
pragma solidity >=0.8.0 <0.9.0;

abstract contract Indexed {
    // @TODO adopt ERC-7201 for directly call data from storage by `eth_getStorageAt` instead `eth_call`.
    uint256 public DEPLOYED_BLOCKNUMBER;
    uint256 public LASTSEEN_BLOCKNUMBER;

    constructor() {
        DEPLOYED_BLOCKNUMBER = _blockNumberProvider();
        LASTSEEN_BLOCKNUMBER = _blockNumberProvider();
    }

    /**
     * @notice some L2 use precompiled contract to get current block number.
     * @dev override this function if the network not use `block.number`.
     */
    function _blockNumberProvider() internal view virtual returns (uint256) {
        return block.number;
    }

    /**
     * @dev stamp last seen block number.
     */
    function _stamp() internal {
        LASTSEEN_BLOCKNUMBER = _blockNumberProvider();
    }
}

Nice to Have

Use ERC-7201 so indexed call eth_getStorageAt instead of eth_call to avoid EVM execution.