`val` vs `var` — what’s the difference?

Deep dive

`val` means the reference can’t be reassigned after initialization. `var` means you can point it to a different value later.

That’s about the *reference*, not the object:

• `val list = mutableListOf(1)` still allows `list.add(2)`.

Practical guidance

• Prefer `val` by default (clearer intent, fewer accidental reassignments).
• Use `var` only when reassignment is part of the logic.

Example

val xs = mutableListOf(1)
xs.add(2)      // OK
// xs = mutableListOf(3) // not OK

var n = 1
n = 2          // OK

Common pitfalls

• Confusing `val` with deep immutability.
• Using `var` “just in case” and making code harder to reason about.