Private

Declarations are public by default: any file in the same module, or any file that imports the module, can use them. Marking a declaration private restricts its use to the module it's declared in: any file in the same module can use it, but a file that merely imports the module gets a warning when using it. private can be applied to struct members, functions, global variables, and types.

struct Settings {
    private int retries;
}

private int defaultRetries() {
    return 3;
}

void main() {
    // Using private declarations is fine in the file they're declared in.
    var settings = Settings(retries = defaultRetries());
    println(settings.retries); // prints 3
}

Using a private declaration from another module produces a warning, not an error: private marks an implementation detail, but nothing stops you from using it if you really need to.