Structs & Records

Structs in Wysna represent product types (records) containing named fields. They are the primary tool for modeling domain entities with explicit, type-checked schemas.

Defining a Struct

Declare a struct using the struct keyword followed by field names and their explicit types:

struct UserProfile {
    id: int
    username: str
    email: str
    is_active: bool
}

---

Instantiation

Structs are instantiated by specifying named field values:

struct UserProfile {
    id: int
    username: str
    email: str
    is_active: bool
}

fn main() -> unit {
    let user = UserProfile {
        id: 101,
        username: "washo",
        email: "washo@wysofia.com",
        is_active: true,
    }

    print("User ID:", user.id)
    print("Username:", user.username)
}

Every field declared in the struct must be provided upon initialization. Field initialization order does not have to match declaration order.

---

Immutability and Modifying Fields

Just like scalar types, fields of a struct cannot be reassigned if the variable binding was created with let:

struct UserProfile {
    id: int
    username: str
    email: str
    is_active: bool
}

fn main() -> unit {
    let admin = UserProfile {
        id: 1,
        username: "admin",
        email: "admin@internal",
        is_active: true,
    }

    # admin.is_active = false  # Compile Error: Cannot mutate fields of immutable binding `admin`

    let mut editable_user = admin
    editable_user.is_active = false  # Permitted! Triggers CoW for fields if shared.
    print("Admin active:", admin.is_active)             # true
    print("Editable active:", editable_user.is_active)  # false
}

---

Nested Structs

Structs can be composed hierarchically:

struct Coordinates {
    lat: float
    lon: float
}

struct LocationMarker {
    name: str
    coords: Coordinates
}

fn main() -> unit {
    let loc = LocationMarker {
        name: "Quito, Ecuador",
        coords: Coordinates {
            lat: -0.1807,
            lon: -78.4678,
        },
    }
    print("Location:", loc.name, loc.coords.lat, loc.coords.lon)
}