當 ERC20 Token 越發越多了，有沒有辦法做一個跨 Token 的交易呢？答案是可以的！今天就讓我們來看看 Token Exchange 要怎麼做吧！

本次的 Example 一樣感謝我的朋友 polarjack 給予程式碼建議。

本日合約:

pragma solidity ^0.4.25;

import "browser/IERC20.sol";

contract TokenExchange {
    // From => UserA, TokenA
    address fromAddress;
    address fromToken;
    uint256 fromAmount;
    // To => UserB, TokenB
    address toToken;
    uint256 toAmount;
    
    // 假設 UserA 已經 Approve
    function CreateExchange(
        address _fromToken, uint256 _fromAmount,
        address _toToken, uint256 _toAmount) public {
            require(IERC20(_fromToken).transferFrom(msg.sender, this, _fromAmount));
            fromAddress = msg.sender;
            fromToken = _fromToken;
            fromAmount = _fromAmount;
            toToken = _toToken;
            toAmount = _toAmount;
        }
    
    function DoChange() public {
        require(IERC20(toToken).transferFrom(msg.sender, this, toAmount));
        IERC20(fromToken).transfer(msg.sender, fromAmount);
        IERC20(toToken).transfer(fromAddress, toAmount);
    }
}

本日影片:
https://youtu.be/1CvTpXEProc

Smart Contract 實戰教學播放清單：
https://www.youtube.com/playlist?list=PLHmOMPRfmOxSJcrlwyandWYiuP9ZAMYoF