void fillRange(int start, int end, [ E fillValue ])

Sets the objects in the range start inclusive to end exclusive to the given fillValue.

The provide range, given by start and end, must be valid. A range from start to end is valid if 0 <= start <= end <= len, where len is this list's length. The range starts at start and has length end - start. An empty range (with end == start) is valid.

Source

void fillRange(int start, int end, [E fillValue]) {
  throw new UnsupportedError("Cannot modify an immutable List.");
}