> ## Documentation Index > Fetch the complete documentation index at: https://docs.syntblaze.com/llms.txt > Use this file to discover all available pages before exploring further. # Dart Set A `Set` in Dart is an iterable collection of unique objects. It enforces element uniqueness by evaluating the equality of its items using their `==` operator and `hashCode` properties. Attempting to add a duplicate value to a `Set` is a no-op; the collection remains unchanged and no exception is thrown. By default, Dart set literals instantiate a `LinkedHashSet`, which maintains insertion order while providing amortized constant-time `O(1)` complexity for add, remove, and lookup operations. ## Syntax and Initialization Sets are typically created using set literals `{}` or explicitly typed constructors. Because Dart uses `{}` for both sets and maps, creating an empty set requires explicit type annotations to prevent the compiler from inferring a `Map`. ```dart theme={"dark"} // Set literal with type inference var primaryColors = {'red', 'green', 'blue'}; // Inferred as Set // Explicitly typed Set literal Set fibonacci = {1, 2, 3, 5, 8}; // Creating an empty Set var emptySet = {}; Set anotherEmptySet = {}; // Anti-pattern: This creates a Map, not a Set var notASet = {}; ``` ## Core Operations The `Set` API provides standard collection mutations and lookups. ```dart theme={"dark"} var nodes = {'A', 'B'}; // Addition nodes.add('C'); // Returns true (added) nodes.add('A'); // Returns false (duplicate, ignored) nodes.addAll({'D', 'E'}); // Adds multiple elements // Removal nodes.remove('B'); // Returns true if element existed and was removed nodes.clear(); // Empties the set // Lookup bool exists = nodes.contains('C'); ``` ## Mathematical Set Operations Dart provides built-in methods for standard mathematical set theory operations, returning new `Set` instances without mutating the originals. ```dart theme={"dark"} var setA = {1, 2, 3, 4}; var setB = {3, 4, 5, 6}; // Union: Combines all unique elements from both sets // Result: {1, 2, 3, 4, 5, 6} var union = setA.union(setB); // Intersection: Yields elements present in both sets // Result: {3, 4} var intersection = setA.intersection(setB); // Difference: Yields elements in setA that are not in setB // Result: {1, 2} var difference = setA.difference(setB); ``` ## Alternative Implementations While `LinkedHashSet` is the default, the `dart:collection` library provides alternative implementations with different performance and ordering guarantees: ```dart theme={"dark"} import 'dart:collection'; // HashSet: Unordered. Iteration order is not guaranteed. // Marginally faster than LinkedHashSet as it doesn't maintain pointers for insertion order. var hashSet = HashSet(); // SplayTreeSet: A self-balancing binary search tree. // Elements are iterated in sorted order according to their `compareTo` method // or a provided Comparator. Operations are O(log n). var treeSet = SplayTreeSet(); ``` ## Spread Operator and Control Flow Sets fully support Dart's spread operator (`...`), null-aware spread operator (`...?`), and collection `if`/`for` constructs for declarative composition. ```dart theme={"dark"} var baseConfig = {'host', 'port'}; bool includeAuth = true; var finalConfig = { ...baseConfig, if (includeAuth) 'credentials', for (var i = 1; i <= 3; i++) 'node_$i' }; // Result: {'host', 'port', 'credentials', 'node_1', 'node_2', 'node_3'} ```

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