Forkchoice Ethereum Mainnet

pragma solidity ^0.5.0;

contract Proxy {

    // masterCopy always needs to be first declared variable, to ensure that it is at the same location in the contracts to which calls are delegated.
    address masterCopy;

    /// @dev Constructor function sets address of master copy contract.
    /// @param _masterCopy Master copy address.
    constructor(address _masterCopy)
        public
    {
        require(_masterCopy != address(0), "Invalid master copy address provided");
        masterCopy = _masterCopy;
    }

    /// @dev Fallback function forwards all transactions and returns all received return data.
    function ()
        external
        payable
    {
        // solium-disable-next-line security/no-inline-assembly
        assembly {
            let masterCopy := and(sload(0), 0xffffffffffffffffffffffffffffffffffffffff)
            calldatacopy(0, 0, calldatasize())
            let success := delegatecall(gas, masterCopy, 0, calldatasize(), 0, 0)
            returndatacopy(0, 0, returndatasize())
            if eq(success, 0) { revert(0, returndatasize()) }
            return(0, returndatasize())
        }
    }

    function implementation()
        public
        view
        returns (address)
    {
        return masterCopy;
    }

    function proxyType()
        public
        pure
        returns (uint256)
    {
        return 2;
    }
}