library-manual-delegatecall

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.17;


struct Data {
    uint a;
    uint b;    
}


bytes32 constant LOCATION = keccak256("place");

library fun {
    
    function setA(uint _a) external {
        Data storage ds = diamondStorage();
        ds.a = _a;
    }

    function getA() external view returns (uint) {
        Data storage ds = diamondStorage();
        return ds.a;
    }


    function diamondStorage() internal pure returns (Data storage ds) {
        bytes32 position = LOCATION;
        assembly {
            ds.slot := position
        }
    }
}

interface ifun {
    function setA(uint _a) external;

    function getA() external view returns (uint);
}

contract A {

    address libAddress = 0xd9145CCE52D386f254917e481eB44e9943F39138;

    function setA(uint _a) external {
        (bool success, bytes memory data) =  libAddress.delegatecall(abi.encodeCall(ifun.setA, (_a)));
    }

    function getA() external returns (uint) {
        (bool success, bytes memory data) = libAddress.delegatecall(abi.encodeCall(ifun.getA, ()));
        return abi.decode(data, (uint));
    }
}