30秒学会 Dart 片段 – slice

Returns a new list containing the elements between start and end.
Negative values can be used, indicating an offset from the end of the list.

Use num.isNegative to check if either start or end are negative and normalize their values.
Use List.sublist() with the normalized values to return the desired list.
Omit the optional parameter, end, to use the length of the list as the default.

代码实现

List<T> slice<T>(List<T> lst, int start, [int end]) {
  int _start = start.isNegative ? lst.length + start : start;
  int _end = end != null ? end.isNegative ? lst.length + end : end : lst.length;
  return lst.sublist(_start, _end);
}

使用样例

List<int> n = [1, 2, 3, 4, 5, 6, 7, 8];

slice(n, 5);      // [6, 7, 8]
slice(n, 1, 3);   // [2, 3]
slice(n, 2, -2);  // [3, 4, 5, 6]
slice(n, -4);     // [5, 6, 7, 8]
slice(n, -6, -2); // [3, 4, 5, 6]