Solidity 智能合约代码中的预期未知错误 - Remix

Question

编译器报告下面附上的错误；很奇怪，因为我正在跟随课程的导师，他建议我使用旧版本的混音，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，我无论如何都试过了，没有用；他正在使用 ^0.4.11 我在 ^0.8.4 上运行，即使当我降级到以前的版本时问题仍然存在。

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breaking changes list 0.4 a 到 0.5 之间：

现在不允许使用 constant 作为函数状态可变性修饰符。

---

在 0.8 中，您还可以将函数声明为 view function，它符合 0.4 constant 中定义的状态不变性标准。

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