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

Short answer

List for ordering and index access, Set for unique values, and Map for accessing a value by a key.

Explanation

Choosing the collection expresses the shape of the data and the rules you need (ordering, uniqueness, or mapping a key to a value). A List preserves element order and may contain duplicates, a Set prevents duplicates and suits membership checks, and a Map associates a key with a value, and keys must be suitable for comparison. Do not choose the type just because it is the most common.

Code example

final names = <String>["Ali", "Mona"];
final tags = <String>{"flutter", "dart"};
final scores = <String, int>{"Ali": 90};

Common mistakes

• Using a List and then doing a linear search for a value that should be unique.
• Forgetting that a Map does not behave sensibly with mutable keys.

Follow-up questions

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

Sources

• Dart language — Collections