Collection Literals

Spread

...

...other flattens another iterable into the literal in place. Useful for prepending or appending.

Program

Play the program to assemble a list from a head, tail, and bookend numbers.

spread.dart
Replay: real traced execution (multi-file project)
void main() {
  var head = [1, 2];
  var tail = [3, 4];
  var all = [0, ...head, ...tail, 5];
  print(all);
}

  1. head ← [1, 2]

    1void main() {2  var head = [1, 2];3  var tail = [3, 4];
    values this step[1, 2]head

  2. tail ← [3, 4]

    2var head = [1, 2];3var tail = [3, 4];4var all = [0, ...head, ...tail, 5];
    values this step[3, 4]tail

  3. all ← [0, 1, 2, 3, 4, 5]

    3var tail = [3, 4];4var all = [0, ...head, ...tail, 5];5print(all);
    values this step[0, 1, 2, 3, 4, 5]all[1, 2]head[3, 4]tail

  4. print(all);

    4  var all = [0, ...head, ...tail, 5];5  print(all);6}
    output[0, 1, 2, 3, 4, 5]
    values this step[0, 1, 2, 3, 4, 5]all
spread `...xs` flattens `xs` into the surrounding literal.
null-aware spread Use `...?xs` to skip the spread when `xs` is null.
composition Combine literal elements with spread elements freely.