“返回参数类型字符串存储ref的解决方案”不可隐式转换为预期类型（first返回变量的类型）字符串calldata＆quort'？

Question

我是一个新的合同，没有编码经验。有人可以帮助解决此错误吗？错误消息是：“返回参数类型字符串存储REF并非隐式转换为预期类型（类型的第一返回变量）字符串CallData。”该错误是对GetGreetings函数的响应，即ln 27，col 16，其中“返回消息”；是。

// SPDX-License-Identifier: GPL-3.0-or-later

pragma solidity ^0.8.0;

contract GreetingsContract {
    /** This is a state variable of type string called message. This is an instance variable used to store the greetings message.
    The string data type means that the variable will contain a variable length array of characters. */
    string message;

/** This is a constructor "Greetings" with no paramater and no return value. This is public so that it can be called outside of the contract. 
Solidity lets us define a constructor that will be called only once when the contract is first deployed to the blockchain. 
The constructor does not return any value in the contract. */
    function Greetings() public {
        message =  "I'm ready!";
    }

/** This will take one parameter of type string and the name will be "_message" so we can differentiate with the internal state variable.
We'll only alter the state of the contract to overwrite the internal message with the argument. 
This function will alter the instance variable with the value sent in parameter. This is also public and doesnt return anything. 
This is often the case for functions that modify the state of the contract because there is currently no way to acces the values returned by such a function. */
    function setGreetings(string calldata _message) public {
        message = _message;
    }

/**View will return the string and the message. */
    **function getGreetings() public view returns (string calldata) {
        return message;
    }**
}

Answer 1

function getGreetings() public view returns (string calldata)

calldata 是一个不读取在功能输入中初始化。您可以在不同的方案中返回字符串calldata - 如果您接受字符串calldata 作为输入，然后返回相同的值。

function foo(string calldata inputString) public pure returns (string calldata) {
    return inputString;
}

---

由于您要返回存储属性的值，因此其值从存储 内存（不是 calldata ）。因此，您需要返回字符串内存。

function getGreetings() public view returns (string memory) {
    return message;
}