Values and nullability

fix makes a binding immutable; var allows writes. Public results, parameters and fields have explicit types. Text maps to Java String, Int to int, Array<Int> to Integer[], and IntArray to int[].

pub fun firstName(names: List<Text>?) -> Text = names?[0] ?? "Guest";

pub fun normalizedName(name: Text?) -> Text {
    fix candidate = name;
    if (candidate != null) { return candidate.upper(); }
    return "GUEST";
}

Safe access evaluates the receiver once and skips indexes/arguments on null. Coalescing evaluates the fallback only on null. ??= yields the existing value or assigned fallback. Mutable bindings keep their declared nullable type after writes; refine a fix value or coalesce explicitly. A null receiver is distinct from an empty list: safe indexing retains Java bounds behavior.

Arithmetic operands must have matching numeric types, with Java promotion of Byte, Short and Char to Int. Checked explicit conversions include toByte(), toInt() and toLong(). upper() and lower() use Locale.ROOT.

Casts and generic nullability

value as Text checks the JVM type and rejects null with ClassCastException. Cast to Text? when null is an accepted result. The operand is evaluated once. Generic constructor arguments are checked against their instantiated types; Box<Text>(nullableName) is rejected, while Box<Text?>(nullableName) is allowed. Inferred Kalm constructor type arguments and inherited Java members preserve nullable element types.