Skip to main content
A Set in Dart is a collection of unique items. It implements the Iterable interface and ensures that no two elements within the collection are equal according to the == operator. While the theoretical concept of a set is unordered, Dart’s default implementation (LinkedHashSet) preserves the insertion order of elements during iteration.

​
Declaration and Initialization

Sets can be initialized using set literals or the Set constructor. Dart infers the type of the Set based on its elements unless explicitly typed.

​
Set Literals

Set literals use curly braces {}. 
// Inferred as Set<String>
var halogens = {'fluorine', 'chlorine', 'bromine', 'iodine', 'astatine'};

// Explicitly typed
Set<int> primeNumbers = {2, 3, 5, 7};

​
Empty Set Initialization

Because map literals also use curly braces, an empty pair of braces {} defaults to a Map<dynamic, dynamic>, not a Set. To create an empty Set, you must provide a type argument or explicit variable typing. 
var names = <String>{}; // Creates an empty Set<String>
Set<String> votes = {}; // Creates an empty Set<String>

var invalidSet = {};    // Creates a Map<dynamic, dynamic>

​
Uniqueness and Equality

The Set enforces uniqueness using the object’s hashCode and == operator. If an attempt is made to add an element that is already present, the Set remains unchanged, and the operation returns false (specifically for the add method). 
var numbers = {1, 2, 3};

// Attempting to add a duplicate
bool added = numbers.add(1); 

print(added);   // false
print(numbers); // {1, 2, 3}

​
Set Algebra

Dart provides built-in methods to perform mathematical set operations. These methods return a new Set instance containing the result. 
final setA = {1, 2, 3, 5};
final setB = {1, 5, 7, 9};

// Union: Elements in A or B (or both)
print(setA.union(setB)); // {1, 2, 3, 5, 7, 9}

// Intersection: Elements in both A and B
print(setA.intersection(setB)); // {1, 5}

// Difference: Elements in A but not in B
print(setA.difference(setB)); // {2, 3}

​
Element Management

Elements are manipulated via methods defined in the Set class and the Iterable interface. Unlike List, elements in a Set cannot be accessed by an integer index (e.g., set[0] is invalid). 
var elements = {'hydrogen', 'helium'};

// Checking existence
print(elements.contains('hydrogen')); // true

// Adding multiple items
elements.addAll(['lithium', 'beryllium']);

// Removing items
elements.remove('helium');

// Iteration
for (final element in elements) {
  print(element);
}

​
Spread Operators

Dart supports the spread operator (...) and the null-aware spread operator (...?) to insert multiple elements from another collection into a Set. 
var setA = {1, 2};
var setB = {3, 4};
var nullableSet;

var combined = {0, ...setA, ...setB};   // {0, 1, 2, 3, 4}
var safeCombine = {0, ...?nullableSet}; // {0}

​
Conversion

Sets can be created from other iterables using the toSet() method, which effectively deduplicates elements from lists or other collections. 
var duplicateList = [1, 2, 2, 3, 1];
var uniqueSet = duplicateList.toSet(); // {1, 2, 3}
var backToList = uniqueSet.toList();   // [1, 2, 3]
Master Dart with Deep Grasping Methodology!Learn More