@Override
    public void seek(PositionProvider index, ReadPhase readPhase) throws IOException {
      // Only our parent class can call this.
      throw new IOException("Should never be called");
    }
We choose to use a toy programming language, so we cannot use multiple inheritance.
If we could, we could have this inherit TreeReader to contain the common impl, and then
have e.g. SettableIntTreeReader inherit both Settable... and Int.. TreeReader-s.
Instead, we have a settable interface that the caller will cast to and call setBuffers.
ql/src/java/org/apache/hadoop/hive/ql/io/orc/encoded/EncodedTreeReaderFactory.java