process method

IList<T> process({ bool test(IList<T> list, int index, T item)?, required Iterable<T>? convert(IList<T> list, int index, T item), })

Allows for complex processing of a list.

Iterates through each item. If the item satisfies the provided test, replace it with applying convert. Otherwise, keep the item unchanged. If test is not provided, it will apply convert to all items.

Function convert can:

• Keep the item unchanged by returning null.
• Remove an item by returning an empty iterable.
• Convert an item to a single item by returning an iterable with an item.
• Convert an item to many items, by returning an iterable with multiple items.

If no items satisfy the test, or if convert kept items unchanged, process will return the same list instance.

Implementation

IList<T> process({
  bool Function(IList<T> list, int index, T item)? test,
  required Iterable<T>? Function(IList<T> list, int index, T item) convert,
}) {
  bool any = false;
  List<T> result = [];
  int _length = length;
  for (int index = 0; index < _length; index++) {
    T item = this[index];
    var satisfiesTest = (test == null) || test(this, index, item);
    if (!satisfiesTest)
      result.add(item);
    else {
      var converted = convert(this, index, item);

      // Keep the item unchanged by returning `null`.
      if (converted == null) {
        result.add(item);
      }
      // Remove an item by returning an empty iterable.
      else if (converted.isEmpty) {
        any = true;
      }
      // Convert an item to a single item by returning an iterable with an item.
      else if (converted.length == 1) {
        var newItem = converted.first;
        result.add(newItem);
        if (!identical(item, newItem)) any = true;
      }
      // Convert an item to many items, by returning an iterable with multiple
      else {
        result.addAll(converted);
        any = true;
      }
    }
  }
  return any ? IList._unsafeFromList(result, config: config) : this;
}