Dart SetBase
last modified April 4, 2025
In Dart, SetBase is an abstract base class for sets that contains common functionality for all Set implementations. It provides operations for working with collections of unique elements.
SetBase implements the core Set interface and provides default implementations for many methods. All elements in a Set must be unique and must have consistent Object.== implementations.
Creating a Set with SetBase
While SetBase is abstract, we can use its concrete implementations like HashSet to demonstrate its functionality.
import 'dart:collection';
void main() {
var numbers = HashSet<int>();
numbers.add(1);
numbers.add(2);
numbers.add(3);
numbers.add(2); // Duplicate, won't be added
print(numbers);
}
We create a HashSet which extends SetBase. We add elements using add(), and duplicates are automatically ignored. The generic type specifies that we're storing integers.
$ dart main.dart
{1, 2, 3}
Set Operations
SetBase provides standard set operations like union, intersection, and difference.
import 'dart:collection';
void main() {
var set1 = HashSet<int>.from([1, 2, 3, 4]);
var set2 = HashSet<int>.from([3, 4, 5, 6]);
print('Union: ${set1.union(set2)}');
print('Intersection: ${set1.intersection(set2)}');
print('Difference: ${set1.difference(set2)}');
}
We demonstrate three fundamental set operations. Union combines elements from both sets, intersection finds common elements, and difference shows elements in set1 not in set2.
$ dart main.dart
Union: {1, 2, 3, 4, 5, 6}
Intersection: {3, 4}
Difference: {1, 2}
Checking Set Contents
SetBase provides methods to check for element existence and set relationships.
import 'dart:collection';
void main() {
var fruits = HashSet<String>.from(['apple', 'banana', 'orange']);
print(fruits.contains('apple')); // true
print(fruits.contains('grape')); // false
print(fruits.containsAll(['apple', 'banana'])); // true
print(fruits.isEmpty); // false
print(fruits.length); // 3
}
We check various properties of the set. contains() checks for single elements while containsAll() verifies multiple elements. isEmpty and length provide size information.
$ dart main.dart true false true false 3
Modifying Sets
SetBase provides methods to modify sets including adding and removing elements.
import 'dart:collection';
void main() {
var colors = HashSet<String>.from(['red', 'green', 'blue']);
// Add elements
colors.add('yellow');
colors.addAll(['purple', 'cyan']);
// Remove elements
colors.remove('green');
colors.removeWhere((color) => color.startsWith('b'));
print(colors);
}
We demonstrate adding single elements with add() and multiple elements with addAll(). We remove elements with remove() and conditionally with removeWhere().
$ dart main.dart
{red, yellow, purple, cyan}
Iterating Over Sets
SetBase provides multiple ways to iterate through set elements.
import 'dart:collection';
void main() {
var primes = HashSet<int>.from([2, 3, 5, 7, 11]);
// Using for-in loop
print('For-in loop:');
for (var prime in primes) {
print(prime);
}
// Using forEach
print('\nForEach:');
primes.forEach((prime) => print(prime));
// Using iterator
print('\nIterator:');
var it = primes.iterator;
while (it.moveNext()) {
print(it.current);
}
}
We demonstrate three iteration methods. The order is undefined as HashSet doesn't guarantee element ordering. All methods provide access to each element in the set.
$ dart main.dart For-in loop: 2 3 5 7 11 ForEach: 2 3 5 7 11 Iterator: 2 3 5 7 11
SetBase with Custom Objects
When using custom objects in sets, proper hashCode and == implementations are crucial.
import 'dart:collection';
class Product {
final String id;
final String name;
Product(this.id, this.name);
@override
bool operator ==(Object other) =>
identical(this, other) ||
other is Product && id == other.id && name == other.name;
@override
int get hashCode => id.hashCode ^ name.hashCode;
}
void main() {
var products = HashSet<Product>();
var p1 = Product('1', 'Laptop');
var p2 = Product('2', 'Phone');
var p3 = Product('1', 'Laptop'); // Same as p1
products.add(p1);
products.add(p2);
products.add(p3);
print('Set size: ${products.length}');
print('Contains p1: ${products.contains(p1)}');
print('Contains p3: ${products.contains(p3)}');
}
The Product class implements == and hashCode to ensure logical equality. p1 and p3 are considered equal, so p3 isn't added to the set. This maintains the uniqueness guarantee of sets.
$ dart main.dart Set size: 2 Contains p1: true Contains p3: true
Best Practices
- Element Uniqueness: Ensure proper == and hashCode for custom elements.
- Immutable Elements: Prefer immutable elements to prevent set corruption.
- Performance: Use contains() for O(1) membership checks.
- Null Safety: Consider non-nullable types for clearer semantics.
Source
This tutorial covered Dart's SetBase with practical examples demonstrating its key features and usage patterns for working with unique element collections.
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