Const Constructors

Const Constructors

About

• Const constructors create compile-time constants.
• Produce canonicalized instances.
• Require immutable objects.
• Enable performance optimizations.

Main Topics

1. Basic Const Constructor

   • **Definition: const` keyword.
   • Example:

     class Point {
       final int x, y;
       const Point(this.x, this.y);
     }

2. Canonicalization

   • **Definition`: Single instance per values.
   • Example:

     const p1 = Point(1,2);
     const p2 = Point(1,2);
     print(identical(p1, p2)); // true

3. Immutable Requirements

   • **Definition: All fields must be final`.
   • Example:

     class Circle {
       final double radius;
       const Circle(this.radius);
     }

4. Performance Benefits

   • **Definition`: Compile-time evaluation.
   • Example:

     const defaultPoint = Point(0,0); // No runtime cost

How to Use

• **Declare: Mark constructor const`
• **Instantiate: Use const` keyword
• **Fields`: Must be final
• **Parameters`: Only constant expressions

How It Works

• **Compile-time`: Evaluated during compilation
• **Canonical`: Single instance per unique values
• **Immutable`: State cannot change

Example Session:

void main() {
  const origin = Point(0,0); // Compile-time constant
  const sameOrigin = Point(0,0); // Same instance
}

Conclusion

Const constructors enable true compile-time constants in Dart, providing memory efficiency and performance benefits for immutable value objects throughout application code.