function MappingList$1() {
  this._array = [];
  this._sorted = true;
  // Serves as infimum
  this._last = {generatedLine: -1, generatedColumn: 0};
}
A data structure to provide a sorted view of accumulated mappings in a
performance conscious manner. It trades a neglibable overhead in general
case for a large speedup in case of mappings being added in order.