Why are constant constructors used?

Constant constructors are used to create objects that will be defined at compile time. This provides the following advantages:

1. Performance: Constant objects are created once during compilation and reused whenever needed. This reduces the overhead of object creation at runtime.
2. Memory savings: Multiple references to the same constant object occupy less memory than creating separate identical objects at runtime.
3. Widget optimization: In Flutter, constant widgets are not rebuilt when the parent’s state changes if their properties do not change. This significantly improves user interface performance.
4. Identity: Constant objects with the same values are considered identical. This allows their use as keys in maps and sets.

Example of creating a constant object:

// Class with a constant constructor
class Point {
  final int x;
  final int y;

  const Point(this.x, this.y);
}

// Using the constant constructor
const p1 = Point(1, 2);
const p2 = Point(1, 2);

// p1 and p2 refer to the same object in memory

Example of using constant widgets in Flutter:

// This widget will not rebuild if its properties (none here) do not change
const Text('Hello, world!');