Fields

A field is a stored value attached to a struct. Each field has a name, a type, and a mutability declaration.

Declaring fields

struct Player {
    let name: String         // immutable after init
    var hp: Int              // mutable
    var inventory: [String]  // mutable
}

let fields are set once, in the initializer, and can't change after. var fields can be reassigned anytime — by methods marked mutating, or by external code holding the struct via var.

Defaults

The memberwise initializer always takes every field. To make a field optional at construction, write your own init and give its parameter a default value:

struct Config {
    var port: Int
    let strict: Bool

    init(strict strict: Bool, port port: Int = 8080) {
        self.port = port;
        self.strict = strict;
    }
}

let c = Config(strict: true);              // port defaults to 8080
let d = Config(strict: false, port: 9000); // override

Defaulted parameters must come after the required ones. See Initializers for the full rules.

Field access

Read a field with dot syntax:

let portInUse = c.port;

Write to a var field — provided you hold the struct via var:

var server = Config(strict: true);
server.port = 9001;   // ok

let fields can't be written even from inside a mutating method. They're sealed at the type level.