這裡列舉是比較常用的其他歸類Utils

Counters

提供只能遞增、遞減或重置的計數器。可以用在元素數量、發布 ERC721 ID 或計算請求 ID。

• 提供 function
  • current 計算到哪
  • increment 遞增
  • decrement 遞減
  • reset 重新設定

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "<https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v4.5.0/utils/Counters.sol>";

contract CountersImpl {
    using Counters for Counters.Counter;

    Counters.Counter private _counter;

    function current() public view returns (uint256) {
        return _counter.current();
    }

    function increment() public {
        _counter.increment();
    }

    function decrement() public {
        _counter.decrement();
    }

    function reset() public {
        _counter.reset();
    }
}

Address

• isContract(account) 是不是合約地址

• sendValue(recipient, amount) 發送金額，錯誤時gas回收(小心使用)

• functionCall(target, data) 呼叫目標合約的function

• functionCall(target, data, errorMessage) 呼叫目標合約的function帶錯誤訊息

• functionCallWithValue(target, data, value)

  呼叫目標合約的function,設定eth 至少多少

• functionCallWithValue(target, data, value, errorMessage)

  呼叫目標合約的function,設定eth 至少多少,帶錯誤訊息

• verifyCallResult(success, returndata, errorMessage) 驗證呼叫結果

• 還有兩個比較原理的呼叫

  Static、Delegate

  Static: 只能呼叫 view, prue 修飾詞的function

  Delegate: msg.sender 一直沿用

  這篇原理講得很完整

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "<https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v4.5.0/utils/Address.sol>";

contract AddressImpl {
    string public sharedAnswer;

    event CallReturnValue(string data);

    function isContract(address account) external view returns (bool) {
        return Address.isContract(account);
    }

    function sendValue(address payable receiver, uint256 amount) external {
        Address.sendValue(receiver, amount);
    }

    function functionCall(address target, bytes calldata data) external {
        bytes memory returnData = Address.functionCall(target, data);
        emit CallReturnValue(abi.decode(returnData, (string)));
    }

    function functionCallWithValue(
        address target,
        bytes calldata data,
        uint256 value
    ) external payable {
        bytes memory returnData = Address.functionCallWithValue(target, data, value);
        emit CallReturnValue(abi.decode(returnData, (string)));
    }

    function functionStaticCall(address target, bytes calldata data) external {
        bytes memory returnData = Address.functionStaticCall(target, data);
        emit CallReturnValue(abi.decode(returnData, (string)));
    }

    function functionDelegateCall(address target, bytes calldata data) external {
        bytes memory returnData = Address.functionDelegateCall(target, data);
        emit CallReturnValue(abi.decode(returnData, (string)));
    }

    // sendValue's tests require the contract to hold Ether
    receive() external payable {}
}

14. Governance

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