operator [] method
Block at index, with code blocks materialized only when requested.
Implementation
DiffReviewBlock operator [](int index) {
RangeError.checkValidIndex(index, this, 'index', length);
final before = threadsBefore(index);
if (before < threadCount && _threadPositions[before] == index) {
return _threads[before];
}
return DiffReviewCodeBlock._(index - before);
}