onGenerateLengthForEach property
If the range is used as the length, the generator randomly determines the lengths in these intervals when it is built.
This means that all results will be of the same length. But if you want the length to be re-selected for each instance (with some performance degradation), then onGenerateLength: true should be.
Implementation
@override
bool get onGenerateLengthForEach => _onGenerateLen;