What is the benefit of spread and collection-if in Dart?

Short answer

Both make building a collection clearer: spread adds the elements of another collection, and collection-if adds them conditionally during construction.

Explanation

Use ... to copy a collection's elements into a new collection, and ...? when the source collection may be null. collection-if and collection-for add elements based on a condition or iteration without creating many temporary lists, which is useful when composing UI data.

Code example

final base = ["Dart"];
final topics = [
  ...base,
  if (includeFlutter) "Flutter",
];

Common mistakes

• Confusing adding the collection itself with adding its elements using spread.
• Using a nullable spread without ...? or a suitable check.

Follow-up questions

• When do you choose List, Set, or Map in Dart?

Sources

• Dart language — Collections