模块化合约

构建合约的模块化方法可帮助您降低复杂性并提高可读性，这将有助于在开发和代码审查期间识别错误和漏洞。如果您单独指定和控制行为或每个模块，则您必须考虑的交互只是模块规范之间的交互，而不是合约的所有其他移动部分。在下面的示例中，合约使用库move的方法来检查地址之间发送的余额是否符合您的预期。通过这种方式，库提供了一个独立的组件，可以正确跟踪账户余额。很容易验证Balances  BalancesBalances库永远不会产生负余额或溢出，并且所有余额的总和在合约的整个生命周期内都是不变量。

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.5.0 <0.9.0;

library Balances {
    function move(mapping(address => uint256) storage balances, address from, address to, uint amount) internal {
        require(balances[from] >= amount);
        require(balances[to] + amount >= balances[to]);
        balances[from] -= amount;
        balances[to] += amount;
    }
}

contract Token {
    mapping(address => uint256) balances;
    using Balances for *;
    mapping(address => mapping (address => uint256)) allowed;

    event Transfer(address from, address to, uint amount);
    event Approval(address owner, address spender, uint amount);

    function transfer(address to, uint amount) external returns (bool success) {
        balances.move(msg.sender, to, amount);
        emit Transfer(msg.sender, to, amount);
        return true;

    }

    function transferFrom(address from, address to, uint amount) external returns (bool success) {
        require(allowed[from][msg.sender] >= amount);
        allowed[from][msg.sender] -= amount;
        balances.move(from, to, amount);
        emit Transfer(from, to, amount);
        return true;
    }

    function approve(address spender, uint tokens) external returns (bool success) {
        require(allowed[msg.sender][spender] == 0, "");
        allowed[msg.sender][spender] = tokens;
        emit Approval(msg.sender, spender, tokens);
        return true;
    }

    function balanceOf(address tokenOwner) external view returns (uint balance) {
        return balances[tokenOwner];
    }
}