【智能合约】delegatecall

• address.delegatecall(bytes calldata)
• delegatecall是将另一个合约的一个函数take over拿来当作自己合约内部函数来用;
• 从函数执行上下文来看，形式上跨合约，实质上没有跨合约，拷贝了message，sender、value不变，但data和gaslimit可以变化
  如下图：
  
  代码实例：

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.13;
// NOTE: Deploy this contract first
contract B {
 // NOTE: storage layout must be the same as contract A
 uint public num;
 address public sender;
 uint public value;
 bytes public cdata;
 function setVars(uint _num) public payable {
 num = _num;
 sender = msg.sender;
 value = msg.value;
 cdata = msg.data;
 }
}
contract A {
 uint public num;
 address public sender;
 uint public value;
 bytes public cdata;
 function setVars(address _contract, uint _num) public payable {
 // A's storage is set, B is not modified.
 (bool success, bytes memory data) = _contract.delegatecall(
 abi.encodeWithSignature("setVars(uint256)", _num)
 );
 }
 function setNum(uint _num) public payable {
 num = _num;
 cdata = msg.data;
 sender = msg.sender;
 value = msg.value;
 }
 function setNumIndirect(uint _num) public {
 setNum(_num);
 }
 function setNumIndirectByCall(uint _num) public {
 address(this).call(abi.encodeWithSignature("setNum(uint256)", _num));
 }
}