Cool use cases for inferred literals in Umka

2023-04-14, 1 minute

Inferred literals have been recently added to Umka. They allow you to omit the type in the struct/array literals. For example, from my game’s codebase:

[]Window{
    Window{
        name: "Test window",
        rect: rect.Rect{ 20, 20, 64, 48 },
        aspect: th.Vf2{ 4, 3 },
        f: fn(this: ^Window) { },
        ctx: null,
        gui: ui.mk(rect.Rect{}, res.getUiStyle()) } }

This can now be converted to the following code:

{ {
        name: "Test window",
        rect: { 20, 20, 64, 48 },
        aspect: { 4, 3 },
        f: { },
        ctx: null,
        gui: ui.mk({}, res.getUiStyle()) } }

This allows Umka code to be much cleaner and compact, although the programmer must make sure the code stays readable.

This new feature also allows you to create functions with keyword arguments. See this greeting function as an example:

type greetKWArgs = struct {
    firstName: str
    lastName: str
    greeting: str
}

fn greet(a: greetKWArgs) {
    if len(a.greeting) == 0 {
        a.greeting = "Hello"
    }

    printf("%s, %s %s\n", a.greeting, a.firstName, a.lastName)
}

greet({ firstName: "Umka" }) // outputs: Hello, Umka

They also allow you to create great struct constructors.

type UserCfg* = struct {
    name: str
    username: str
}

type User* = struct {
    name: str
    email: str
    username: str
    id: int
}

fn mkUser*(email: str, cfg: UserCfg = {}): User {
    if cfg.name == "" {
        cfg.name = sprintf("Guest %d", std.rand() % 1000)
    }

    if cfg.username == "" {
        cfg.username = usernameFromName(cfg.name)
    }

    return {
        name: cfg.name,
        username: cfg.username,
        email: email,
        id: fetchIdByEmail(email) }
}

As you can notice, providing email is required, however the name and the username can be generated by the constructor. For that reason they are specified using the UserCfg struct. id on the other hand, is always generated by the function.