中的可靠预期不明错误- Remix

Question

编译器报告了下面所附的错误；非常奇怪，因为我跟随课程的导师，他建议我使用较旧版本的remix，我在类似的问题中读到，“返回”应该是单数，但他的代码编译没有问题，无论如何，我尝试了，但没有起作用；他使用的是^0.4.11，我正在使用^0.8.4，尽管当我降级到以前的版本时，这个问题仍然存在。

错误：

ParseError: Expected '{' but
got 'constant' -->
tests/pendulum_ico.sol:28:60: |
28 | function 
equity_in_pendulum(address 
investor) external constant 
returns (uint) { | ^^^^^^^^

代码：

pragma solidity ^0.8.3;

contract pendulum_ico {
    
// Introducing the maximum number of Pendulum available for sale

    uint public max_pendulum = 1000000;
    
// Introducing the USD to Pendulum conversion relocatable

    uint public usd_to_pendulum = 1000;
    
// Introducing the total number of Pendulum that have been bought by the investors

    uint public total_pendulum_bought = 0;
    
// Mapping from the investor address to its equity in Pendulum and usd_to_pendulum

    mapping(address => uint) equity_pendulum;
    mapping(address => uint) equity_usd;
    
// Checking if an investor can buy Pendulum

    modifier can_buy_pendulum(uint usd_invested) {
        require (usd_invested * usd_to_pendulum + total_pendulum_bought <= max_pendulum);
        _;
    }
    
// Getting the equity in Pendulum of an investor

    function equity_in_pendulum(address investor) external constant returns (uint) { 
        return equity_pendulum[investor];
    }                             
    
// Getting the equity in USD of an investor

    function equity_in_usd(address investor) external constant returns (uint) {
        return equity_usd[investor];
    }
    
// Buying Pendulum 

    function buy_pendulum(address investor, uint usd_invested) external
    can_buy_pendulum(usd_invested) {
        uint pendulum_bought = usd_invested * usd_to_pendulum;
        equity_pendulum[investor] += pendulum_bought;
        equity_usd[investor] = equity_pendulum[investor] / 1000;
        total_pendulum_bought += hadcoins_bought;
        
    }
    
// Selling Pendulum 

    function sell_pendulum(address investor, uint pendulum_sold) external {
        equity_pendulum[investor] -= pendulum_sold;
        equity_usd[investor] = equity_pendulum[investor] / 1000;
        total_pendulum_bought -= pendulum_sold;
    }
    
}

Answer 1

从0.4 a到0.5之间的打破更改列表：

现在不允许使用constant作为函数状态可变修饰符。

在0.8中，您还可以将函数声明为视图函数，这符合0.4 constant中定义的状态不可变性标准。

function equity_in_pendulum(address investor) external view returns (uint) { 
    return equity_pendulum[investor];
}