fallback.sol

    pragma solidity ^0.6.0;

    contract DelegateProxy {
        address internal implementation;
        
        fallback() external payable {
            address addr = implementation;
        
            assembly {
                calldatacopy(0, 0, calldatasize())
                let result := delegatecall(gas(), addr, 0, calldatasize(), 0, 0)
                returndatacopy(0, 0, returndatasize())
                switch result
                case 0 { revert(0, returndatasize()) }
                default { return(0, returndatasize()) }
            }
        }
    }