Why is this initialization of final fields wrong in Dart?
Günter Zöchbauer already explained the reason for your error.
Here is a workaround:
Data(Step initializer(Map<String,List<double>> dataReferences)) : this._internal(initializer, new Map());Data._internal(initializer, map) : _dataMap = map, _updateStep = initializer(map);
You are reading from _dataMap (initializer(_dataMap)). _datamap is a field of this it is not an argument. You can't read fields from 'this' in constructor initializers as the error message says.