Assignment Between const and final Variables

A const variable can be assigned to a final variable, but not the other way around.

Here’s why:

1. Const to Final:
   • A const variable, being a compile-time constant, can be assigned to a final variable because its value is known at compile time.
   • The final variable will then hold the same immutable value as the const variable.
2. Final to Const:
   • A final variable, while immutable, might not be a compile-time constant. Its value could be determined at runtime.
   • Assigning a final variable to a const variable would violate the const requirement of being known at compile time.

Example:

const pi = 3.14159;
final double circumference = 2 * pi * 5; // Valid

In this example, pi is a const variable, and its value is known at compile time. It’s assigned to the final variable circumference, which is then also a constant value.

However, the following would be invalid:

final DateTime now = DateTime.now();
const DateTime fixedTime = now; // Invalid, now's value is determined at runtime

Here, now is a final variable, but its value is determined at runtime. Assigning it to a const variable would violate the compile-time constant requirement.