step6.sol

pragma solidity ^0.5.1;

contract StorageContract {
    uint counter;
}

contract ProxyContract is StorageContract {
    address internal proxied;
    
    function setLogicContractAddress (address newAddress) public
    {
        proxied = newAddress;
    }
    
    constructor(address _proxied) public {
        proxied = _proxied;
    }
    
    /**
     * Fallback function allowing to perform a delegatecall 
     * to the given implementation. This function will return 
     * whatever the implementation call returns
     */
    function () external payable {
        address addr = proxied;
        assembly {
            let freememstart := mload(0x40)
            calldatacopy(freememstart, 0, calldatasize())
            let success := delegatecall(not(0), addr, freememstart, calldatasize(), freememstart, 32)
            switch success
            case 0 { revert(freememstart, 32) }
            default { return(freememstart, 32) }
        }
    }    
}

contract LogicContract is StorageContract {

    function getcounter () public view returns (uint)
    {
        return counter;
    }
    
    function incrementcounter () public
    {
        counter++;
    }
}