This method is called to decode the contents of the current cell, if
set_state() was previously called with a nullptr "cell" argument. This
allows decoding on demand for subtypes that keep the cell contents in
an encoded state. It does not need to be implemented at all if
set_state() is always called with (cell != nullptr).
REQUIRES: This method is thread-safe.
REQUIRES: Multiple calls to this method return the same value.
This method is called to decode the contents of the current cell, if set_state() was previously called with a nullptr "cell" argument. This allows decoding on demand for subtypes that keep the cell contents in an encoded state. It does not need to be implemented at all if set_state() is always called with (cell != nullptr).
REQUIRES: This method is thread-safe. REQUIRES: Multiple calls to this method return the same value.