SingleStateQueue: Add last method to Mutator

            return mShared->mAck - sequence >= 0;

        }

        // returns the last value written (or the contents of the shared buffer after initialization

        // if no value was written).

        T last() const

        {   // assume no sequence check required - we are the writer.

            return mShared->mValue;

        }

    private:

        int32_t     mSequence;

        Shared * const mShared;