convertListToType<T> function

List<T> convertListToType<T>(List origin, { List? discardedList, })

Convert a List from one type to another skipping al those elements not compatible with the target type.

List fool = 'foo', 10, null; List

optional - if a discarded list is passed, the method will add to it all elements of the origin list that are not of the target type. The discarded list must be of the same type of the origin, (or dynamic) and it is cleaned while starting, so any contained value is lost.

List fool = 'foo', 10, null; var discarded = []; List

At 2.12.2 time it can give problem with lists of complex sub types. I they are inferred by the system, the seems to be ok, if you define a specific type, the sub elements are set as that type. *** open issue request

Implementation

List<T> convertListToType<T>(List origin, {List? discardedList}) {
  var saveDiscarded = false;

  if (discardedList == null) {
    return <T>[
      for (var element in origin)
        if (element is T) element
    ];
  }

  saveDiscarded = true;
  discardedList.clear();

  var ret = <T>[];
  for (var element in origin) {
    if (element is T) {
      ret.add(element);
      continue;
    }
    if (saveDiscarded) {
      discardedList.add(element);
    }
  }
  return ret;
}