YolkValue

The only type that crosses the bridge. An immutable, Sendable value-type enum.

public indirect enum YolkValue: Sendable {
    case null
    case bool(Bool)
    case int(Int)
    case double(Double)
    case string(String)
    case array([YolkValue])
    case object([String: YolkValue])
}

Design rationale

YolkValue is a value type (enum). Nothing that crosses the bridge is a shared reference. This prevents the category of memory bugs where JS holds a reference to a Swift object that has since been deallocated (or vice versa).

Literals

YolkValue conforms to all standard literal protocols:

let v1: YolkValue = "hello"        // .string
let v2: YolkValue = 42             // .int
let v3: YolkValue = 3.14           // .double
let v4: YolkValue = true           // .bool
let v5: YolkValue = nil            // .null
let v6: YolkValue = [1, 2, 3]     // .array
let v7: YolkValue = ["x": 1]      // .object

Codable

YolkValue conforms to Codable. You can encode it to/from JSON if needed, though values normally cross the bridge without serialisation.

let json = try JSONEncoder().encode(someValue)
let back = try JSONDecoder().decode(YolkValue.self, from: json)

Pattern matching

switch value {
case .string(let s): print(s)
case .int(let n):    print(n)
case .null:          print("nothing")
default:             break
}

Safe array access

Collections have a [safe:] subscript to avoid out-of-bounds crashes in generated dispatch code:

let first = args[safe: 0] ?? .null