Extension operator
- Dart course
- Expert
- Lesson 21/47
- 5 min
Learn extension operator overloading.
Extension operator
Extension operator is operator overloading within an extension. The extension VectorOps on Vector { Vector operator +(Vector other) => ... } declaration redefines the + operator for Vector.
Operator overloading allows custom operations with natural syntax: v1 + v2 adds two Vectors. Dart allows overloading many operators like + - * / == < >. Each operator has a fixed signature.
Operator rules
In Dart, each operator has a fixed signature. operator + takes one parameter and the return type is free. operator == must return bool and should be consistent with hashCode when possible.
Some operators cannot be overloaded: =, !, ??, ., ~/ (except ~/=). operator [] and operator []= are used for indexing. Logical operators (&&, ||) cannot be overloaded.
Practice A Vector + operator
Define a Vector class with final int x; final int y; const Vector(this.x, this.y); field and constructor. Define a VectorOps extension on Vector with a Vector operator +(Vector other) => Vector(x + other.x, y + other.y); method. In main create final v = Vector(1, 2) + Vector(3, 4);; print with print('${v.x},${v.y}');.
Starter code
void main() {
// define a Vector class and a VectorOps extension
// print Vector(1,2) + Vector(3,4)
}Sample solution
class Vector {
final int x;
final int y;
const Vector(this.x, this.y);
}
extension VectorOps on Vector {
Vector operator +(Vector other) => Vector(x + other.x, y + other.y);
}
void main() {
final v = Vector(1, 2) + Vector(3, 4);
print('${v.x},${v.y}');
}Expected output
4,6
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match the operators
| Term | Meaning |
|---|---|
operator + |
Addition |
operator == |
Equality |
operator < |
Less than |
operator * |
Multiplication |
2 What must operator == return?
- int
- bool Correct answer
- String
- void
Explanation: operator == must return bool.
3 An operator + declaration
Vector operator +(____ other) => Vector(x + other.x, y + other.y);Vector operator +(Vector other) => Vector(x + other.x, y + other.y);Explanation: operator +(Vector other) adds two Vectors.