diffBookDepth method
Difference book depth
This can be used to update an existing book with incremental changes
Implementation
Stream<DiffBookDepth> diffBookDepth(String symbol) {
final channel = _public('${symbol.toLowerCase()}@depth');
return channel.stream
.map<Map>(_toMap)
.map<DiffBookDepth>((m) => DiffBookDepth.fromMap(m));
}