Take Milo for a walk

Each program's output below is captured from a native build. To edit and run them yourself, install Milo.

Lesson 1 of 13: Immutable by default1. Immutable by default2. Ownership and moves3. Borrowing4. Structs5. Enums and exhaustive match6. Collections7. Errors are values8. Closures and iterators9. Generics, monomorphized10. Interfaces and dynamic dispatch11. Parse JSON into typed values12. Contracts, checked or proven13. Putting it together

Immutable by default

A let binding is immutable; a var is mutable. You opt in to change.

values.milo

fn main(): i32 {
    let name = "Milo"        // immutable
    var count = 0            // mutable
    count = count + 3
    print($"hello from {name}, count = {count}")
    return 0
}

$ milo run values.milo

hello from Milo, count = 3

Takeaway You always know which bindings can change under you: only the ones marked var.

NextOwnership and moves