Is there any difference when declaring a variable of using const vs immutable.

Example:

const     int a = 3;
immutable int b = 4;

const     string c = "Greetings!";
immutable string d = "D Programmers!";

On Friday, 17 October 2025 at 19:49:07 UTC, Brother Bill wrote:

const     int a = 3;
immutable int b = 4;

const     string c = "Greetings!";
immutable string d = "D Programmers!";

Yes, a const declaration types the value as const, whereas an immutable declaration types the value as immutable.

While this is somewhat of an obvious explanation, the differences are subtle.

• A const reference type can point at either a mutable or immutable value. So regardless of where the value is stored, this has implications on where you can pass the value. You cannot pass a const reference to an immutable parameter.
• A non-reference type can be stored as either const or immutable, and it's effectively the same thing (value types such as int can be freely implicitly converted between mutability).
• Taking the address of a const or immutable value keeps the mutability when passing around, and this has implications as to what functions can accept such parameters.

My recommendation is to use immutable for declaring constants. Use const when you will assign to data that might be either immutable or mutable.

-Steve