當一個 ERC20 的合約出了意外，或者是即將要進行主網映射，需要做暫停交易的時候應該怎麼辦呢？
今天就讓我們來探討這個 Pausable 的機制怎麼實作吧！

本日合約:

pragma solidity ^0.4.25;

contract Pausable {
    bool private _paused;
    
    constructor() public {
        _paused = false;
    }
    
    modifier whenPaused() {
        require(_paused);
        _;
    }
    
    modifier whenNotPaused() {
        require(!_paused);
        _;
    }
    
    event Pause(address addr);
    event Unpause(address addr);
    
    function pause() public whenNotPaused returns (bool) {
        _paused = true;
        emit Pause(msg.sender);
        return true;
    }
    
    function unpause() public whenPaused returns (bool) {
        _paused = false;
        emit Unpause(msg.sender);
        return true;
    }
    
    function transfer() public whenNotPaused returns (bool) {
        //...
    }
}

本日影片:
https://youtu.be/KWlnAyn7uLY

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