模塊化合約

構(gòu)建合約的模塊化方法可幫助您降低復(fù)雜性并提高可讀性，這將有助于在開發(fā)和代碼審查期間識別錯誤和漏洞。如果您單獨指定和控制行為或每個模塊，則您必須考慮的交互只是模塊規(guī)范之間的交互，而不是合約的所有其他移動部分。在下面的示例中，合約使用庫move的方法來檢查地址之間發(fā)送的余額是否符合您的預(yù)期。通過這種方式，庫提供了一個獨立的組件，可以正確跟蹤賬戶余額。很容易驗證Balances  BalancesBalances庫永遠不會產(chǎn)生負余額或溢出，并且所有余額的總和在合約的整個生命周期內(nèi)都是不變量。

// 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];
    }
}