# 撰寫可升級合約

## 部署可升级合约

1. 不寫 `constructor` 寫 init function，並確保此 function 只能被執行依次

contract MyContract {
    uint256 public x;
    bool private initialized;

    function initialize(uint256 _x) public {
        require(!initialized, "Contract instance has already been initialized");
        initialized = true;
        x = _x;
    }
}

2. 所有調用的父合約都不能有 constructor

import "@openzeppelin/contracts-upgradeable/proxy/utils/Initializable.sol";

contract BaseContract is Initializable {
    uint256 public y;

    function initialize() public initializer {
        y = 42;
    }
}

contract MyContract is BaseContract {
    uint256 public x;

    function initialize(uint256 _x) public initializer {
        BaseContract.initialize(); // Do not forget this call!
        x = _x;
    }
}

2. 使用可升級的智能合約庫
``@openzeppelin/contracts-upgradeable`

// @openzeppelin/contracts-upgradeable/contracts/token/ERC20/ERC20Upgradeable.sol
pragma solidity ^0.6.0;
  ...
contract ERC20Upgradeable is Initializable, ContextUpgradeable, IERC20Upgradeable {
  ...
    string private _name;
    string private _symbol;
    uint8 private _decimals;

    function __ERC20_init(string memory name, string memory symbol) internal initializer {
        __Context_init_unchained();
        __ERC20_init_unchained(name, symbol);
    }

    function __ERC20_init_unchained(string memory name, string memory symbol) internal initializer {
        _name = name;
        _symbol = symbol;
        _decimals = 18;
    }
  ...
}

4. 避免直接設定初始值

contract xxx {
    string test = 13; // X
    
    function initialize() public initializer {
        test = 42; // O
    }
}

5. 避免建立實例並賦值，可以使用傳參的方式

contract wrong is Initializabl{
    ERC20 public token;

    function initialize() public initializer {
        token = new ERC20("Test", "TST"); // X
    }
}

contract right is Initializabl {
    IERC20Upgradeable public token;

    function initialize(IERC20Upgradeable _token) public initializer {
        token = _token;
    }
}

6. 避免在合約中使用 `selfdestruct`, `delegatecall`
7.

## 升级已部署的合约

## 管理代理管理员权限

## 在测试中使用

### Reference
https://docs.openzeppelin.com/upgrades-plugins/1.x/writing-upgradeable
https://blog.openzeppelin.com/proxy-patterns/