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learn...delegate_demo.sol

// SPDX-License-Identifier: GPL-3.0

pragma solidity ^0.7.0;

contract delegate_demo {
    Erc20Util util;
    constructor(address _util){
        util = Erc20Util(_util);
    }
    
    function SetUtil(address _util) public {
        util = Erc20Util(_util);
    }

    event DelegateBatchTransfer20(address indexed erc20, address to, uint256 amount);
    event DelegateCall(bool success, bytes result);

    function delegate_BatchTransfer20(address util, address erc20, address to, uint256 amount) public {
        (bool success,bytes memory result) = util.delegatecall(abi.encodeWithSignature("BatchTransfer20(address,address,uint256)", erc20, to, amount));
        emit DelegateBatchTransfer20(erc20, to, amount);
    }

    function delegate_BatchTransfer202(address erc20, address to, uint256 amount) public {
        util.BatchTransfer20(erc20, to, amount);
        emit DelegateBatchTransfer20(erc20, to, amount);
    }

    function delegate_call(address util, string  calldata data) public {
        (bool success, bytes memory result) = util.delegatecall(abi.encodeWithSignature(data));
        emit DelegateCall(success, result);
    }
}


contract Erc20Util {
    function BatchTransfer20(address erc20, address to, uint256 amount) public {
        IERC20 _erc20 = IERC20(erc20);
        _erc20.transferFrom(msg.sender, to, amount);
        _erc20.transferFrom(msg.sender, to, amount);
    }
}


interface IERC20 {
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);
}