Creates a fixed-length list of the given length, and initializes the
value at each position with fill:
new List<int>.filled(3, 0); // [0, 0, 0]
The length must be a non-negative integer.
If the list is growable, changing its length will not initialize new
entries with fill. After being created and filled, the list is
no different from any other growable or fixed-length list
created using List.
Source
external factory List.filled(int length, E fill, {bool growable: false});