在0.6.8版本的solidity中使用delegatecall进行合约升级

在0.4.26版本的solidity中，delegatecall的返回值只有1个，表示delegatecall是否调用成功的布尔变量。
在0.6.8版本的solidity中，delegatecall的返回值有2个，一个是表示delegatecall是否调用成功的布尔变量，另一个则是被调用函数的返回值。

通过delegatecall调用逻辑合约来修改数据合约中的状态变量，从而实现数据和逻辑分离。后面可以通过升级逻辑合约来改变业务逻辑，但数据合约不能升级。

下面通过例子来说明在0.6.8版本的solidity中如何使用delegatecall进行合约升级。

合约代码：

pragma solidity ^0.6.8; 


// 数据合约
contract DataContract {    

    uint256 public num1;
    uint256 public num2;
    uint256 public num3;
    address public issuer;

    
    
    event Log(string str, bool result);
    event Log2(string str, uint256 result);
    
    constructor() public {
        issuer = msg.sender;
        num1 = 1;
        num2 = 2;
        num3 = 3;
    }
    
    function callLogicContract(address logicContractAddr) public {

        bool r;
        bytes memory s;

        // 通过delegatecall调用逻辑合约来修改数据合约中的状态变量，从而实现数据和逻辑分离。后面可以通过升级逻辑合约来改变业务逻辑，但数据合约不能升级
        (r, s) = logicContractAddr.delegatecall(abi.encodeWithSignature("test(address)", this)); 
        emit Log("delegatecall return ", r);  // r为true或false
        uint256 result = bytesToUint(s);
        emit Log2("test() return ", result);
    } 

    function bytesToUint(bytes memory b) public pure returns (uint256){

        uint256 number;
        for(uint i= 0; i

升级合约后，调用合约LogicContract2的test函数的日志输出

logs 	[
	{
		"from": "0x4abfb9d52f63834b2a30b42202be4f43c8cc8b48",
		"topic": "0xdd970dd9b5bfe707922155b058a407655cb18288b807e2216442bca8ad83d6b5",
		"event": "Log",
		"args": {
			"0": "after upgrading contract, num3=",
			"1": "9000",
			"str": "after upgrading contract, num3=",
			"num": "9000",
			"length": 2
		}
	},
	{
		"from": "0x4abfb9d52f63834b2a30b42202be4f43c8cc8b48",
		"topic": "0x953bb7c6c7f939308a523ff2ce38248d9a26e7e8212c5f982fd8dffaca3fc523",
		"event": "Log2",
		"args": {
			"0": "dataContract=",
			"1": "0x4ABFb9D52f63834b2A30B42202Be4F43C8CC8b48",
			"str": "dataContract=",
			"addr": "0x4ABFb9D52f63834b2A30B42202Be4F43C8CC8b48",
			"length": 2
		}
	},
	{
		"from": "0x4abfb9d52f63834b2a30b42202be4f43c8cc8b48",
		"topic": "0x953bb7c6c7f939308a523ff2ce38248d9a26e7e8212c5f982fd8dffaca3fc523",
		"event": "Log2",
		"args": {
			"0": "caller=",
			"1": "0xC264358Ef94b48B62e7F94ce10795255f8b9EED7",
			"str": "caller=",
			"addr": "0xC264358Ef94b48B62e7F94ce10795255f8b9EED7",
			"length": 2
		}
	},
	{
		"from": "0x4abfb9d52f63834b2a30b42202be4f43c8cc8b48",
		"topic": "0x52dd9d08c343f72c69027ade2a075f6242dba2eeca3a3c61bfd8d00d32f6bd20",
		"event": "Log",
		"args": {
			"0": "delegatecall return ",
			"1": true,
			"str": "delegatecall return ",
			"result": true,
			"length": 2
		}
	},
	{
		"from": "0x4abfb9d52f63834b2a30b42202be4f43c8cc8b48",
		"topic": "0x0c231cace93330e81aabd308eaecd9a98302e543efad0c88d0b99732e7c2ef5f",
		"event": "Log2",
		"args": {
			"0": "test() return ",
			"1": "9000",
			"str": "test() return ",
			"result": "9000",
			"length": 2
		}
	}
]