數組切片

數組切片是數組連續(xù)部分的視圖。它們寫成x[start:end], wherestart和 end是導致 uint256 類型（或隱式轉換為它）的表達式。切片的第x[start]一個元素是 ，最后一個元素是。x[end - 1]

如果start大于end或end大于數組的長度，則拋出異常。

兩者start和end都是可選的：默認start為數組的長度。0end

數組切片沒有任何成員。它們可以隱式轉換為其基礎類型的數組并支持索引訪問。索引訪問在底層數組中不是絕對的，而是相對于切片的開頭。

數組切片沒有類型名稱，這意味著沒有變量可以將數組切片作為類型，它們只存在于中間表達式中。

筆記

到目前為止，數組切片僅針對 calldata 數組實現。

數組切片對于 ABI 解碼函數參數中傳遞的輔助數據很有用：

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.8.5 <0.9.0;
contract Proxy {
    /// @dev Address of the client contract managed by proxy i.e., this contract
    address client;

    constructor(address client_) {
        client = client_;
    }

    /// Forward call to "setOwner(address)" that is implemented by client
    /// after doing basic validation on the address argument.
    function forward(bytes calldata payload) external {
        bytes4 sig = bytes4(payload[:4]);
        // Due to truncating behaviour, bytes4(payload) performs identically.
        // bytes4 sig = bytes4(payload);
        if (sig == bytes4(keccak256("setOwner(address)"))) {
            address owner = abi.decode(payload[4:], (address));
            require(owner != address(0), "Address of owner cannot be zero.");
        }
        (bool status,) = client.delegatecall(payload);
        require(status, "Forwarded call failed.");
    }
}