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prefer_collection_literals

Contents
Stable
Recommended
Fix available

Use collection literals when possible.

Details

#

DO use collection literals when possible.

BAD:

dart
var addresses = Map<String, String>();
var uniqueNames = Set<String>();
var ids = LinkedHashSet<int>();
var coordinates = LinkedHashMap<int, int>();

GOOD:

dart
var addresses = <String, String>{};
var uniqueNames = <String>{};
var ids = <int>{};
var coordinates = <int, int>{};

EXCEPTIONS:

When a LinkedHashSet or LinkedHashMap is expected, a collection literal is not preferred (or allowed).

dart
void main() {
  LinkedHashSet<int> linkedHashSet =  LinkedHashSet.from([1, 2, 3]); // OK
  LinkedHashMap linkedHashMap = LinkedHashMap(); // OK

  printSet(LinkedHashSet<int>()); // LINT
  printHashSet(LinkedHashSet<int>()); // OK

  printMap(LinkedHashMap<int, int>()); // LINT
  printHashMap(LinkedHashMap<int, int>()); // OK
}

void printSet(Set<int> ids) => print('$ids!');
void printHashSet(LinkedHashSet<int> ids) => printSet(ids);
void printMap(Map map) => print('$map!');
void printHashMap(LinkedHashMap map) => printMap(map);

Enable

#

To enable the prefer_collection_literals rule, add prefer_collection_literals under linter > rules in your analysis_options.yaml file:

analysis_options.yaml
yaml
linter:
  rules:
    - prefer_collection_literals

If you're instead using the YAML map syntax to configure linter rules, add prefer_collection_literals: true under linter > rules:

analysis_options.yaml
yaml
linter:
  rules:
    prefer_collection_literals: true

Unless stated otherwise, the documentation on this site reflects Dart 3.8.1. Page last updated on 2025-03-07. View source or report an issue.