Wrap input in Buffer

[renggli]

Currently code is scattered with type-checks on the parsed input being a String or a List. Having a buffer could avoid this problem and enable further extensibility on the data being parsed.

/// An immutable parse buffer.
abstract class Buffer<E, S> {

  ///
  factory Buffer.from(Object input) {
    if (input is String) {
      return new _StringBuffer(input, input.length);
    } else if (input is List) {
      return new _ListBuffer(input, input.length);
    }
  }

  /// Return the underlying data structure.
  S data;

  /// Return the size of the buffer.
  int get size;

  /// Return the element at position [value].
  E operator [](int index);

  /// Return the sequence from [start] to [stop].
  S sequence(int start, int stop);

}

class _StringBuffer implements Buffer<int, String> {

  @override
  final String data;

  @override
  final int length;

  _StringBuffer(this.data, this.length);

  @override
  int operator [](int index) => data.codeUnitAt(index);

  @override
  String sequence(int startIndex, int stopIndex) => data.substring(startIndex, stopIndex);

}

class _ListBuffer<T> implements Buffer<T, List<T>> {

  @override
  final List<T> data;

  @override
  final int length;

  _ListBuffer(this.data, this.length);

  @override
  T operator [](int index) => data[index];

  @override
  List<T> sequence(int startIndex, int stopIndex) => data.sublist(startIndex, stopIndex);

}

[renggli]

No longer relevant, since PetitParser dropped support for non-string parsing.