Dart Collections: Dart Spread Operations

In Dart, spread operations allow you to easily combine or create collections by spreading the elements of another collection. There are two types of spread operations: spread (...) and null-aware spread (...?).

Spread (...) Operation:

Lists:

void main() {
  List<int> numbers = [1, 2, 3];
  List<int> moreNumbers = [4, 5, 6];

  // Combining lists using spread operation
  List<int> combinedNumbers = [...numbers, ...moreNumbers];

  print(combinedNumbers);  // Output: [1, 2, 3, 4, 5, 6]
}

Sets:

void main() {
  Set<int> setA = {1, 2, 3};
  Set<int> setB = {3, 4, 5};

  // Combining sets using spread operation
  Set<int> combinedSet = {...setA, ...setB};

  print(combinedSet);  // Output: {1, 2, 3, 4, 5}
}

Maps:

void main() {
  Map<String, int> mapA = {'a': 1, 'b': 2};
  Map<String, int> mapB = {'b': 3, 'c': 4};

  // Combining maps using spread operation
  Map<String, int> combinedMap = {...mapA, ...mapB};

  print(combinedMap);  // Output: {a: 1, b: 3, c: 4}
}

Null-aware Spread (...?) Operation:

The null-aware spread operator (...?) is used to spread elements only if the source collection is not null.

Lists:

void main() {
  List<int>? numbers = [1, 2, 3];
  List<int>? moreNumbers = null;

  // Combining lists using null-aware spread operation
  List<int> combinedNumbers = [...?numbers, ...?moreNumbers ?? []];

  print(combinedNumbers);  // Output: [1, 2, 3]
}

Sets:

void main() {
  Set<int>? setA = {1, 2, 3};
  Set<int>? setB = null;

  // Combining sets using null-aware spread operation
  Set<int> combinedSet = {...?setA, ...?setB ?? <int>{}};

  print(combinedSet);  // Output: {1, 2, 3}
}

Maps:

void main() {
  Map<String, int>? mapA = {'a': 1, 'b': 2};
  Map<String, int>? mapB = null;

  // Combining maps using null-aware spread operation
  Map<String, int> combinedMap = {...?mapA, ...?mapB ?? <String, int>{}};

  print(combinedMap);  // Output: {a: 1, b: 2}
}

Spread operations are useful for creating new collections, combining existing ones, and handling cases where collections might be null. They provide a concise and readable way to manipulate collections in Dart.