Classes

Just like Structs, classes are reusable bits of code that contain data and provide functionality in a scoped and secure way. Unlike structs, which are value types, classes in Iona are always reference types.

A struct is defined like this:

class User {
    ...
}

Classes may contain properties (variables) and functions (both reading and mutating):

class Ticket {
    let price = 22.99
    let seat = 3
    let row = 23
}

class TicketServer {
    var leftTickets: [Ticket] = [Ticket { price: 22.99, seat: 2, row: 23 }]

    mut fn buyTicket(row: Int, seat: Int) {
        // Find ticket and remove it from the array ...
        self.leftTickets.remove(...)
    }

    fn availableTickets() -> [Ticket]& {
        return self.leftTickets
    }
}

note

Functions inside classes are called methods.

They automatically have access to self. self always points to the object itself.

Initialisation

Every class needs at least one init that assigns all properties:

class Ticket {
    let price: Float

    init(price: Float) {
        self.price = price
    }
}

var ticket = Ticket(price: 23.99)

note

There is no auto-generated init for classes.

One init may call another init, but there must be one default init that all other inits call:

class Ticket {
    let price: Float

    default init(price: Float) {
        self.price = price
    }

    init(price: Float, tax: Float) {
        init(price: price - (price * tax))
    }
}

var ticket = Ticket(price: 23.99, tax: 0.1)

When using init, every property must be initialised:

class Ticket {
    let price: Float
    let seat: Int

    init(price: Float) {
        self.price = price
        // Error: seat was not initialised in init
    }
}

var ticket = Ticket(price: 23.99)

Inheritance

Classes may either conform to a contract (implementing its properties and methods) or inherit from another class (subclassing).

Subclassing:

class Device {
    let storage: Float

    init(storage: Float) {
        self.storage = storage
    }

    fn readFrom(index: Int) {
        ...
    }
}

class Phone: Device {
    init {
        super.init(storage: 512)
    }
}


var phone = Phone()
phone.readFrom(index: 0)

Conformance:

contract Storage {
    var storage: Int { get }

    fn store(index: Int)
}

class SolidStateDrive: Storage {
    var storage: Int

    init(size: Int) {
        self.storage = size
    }

    fn store(index: Int) {
        ...
    }
}