AutoObjectiveCBridgeable

AutoObjectiveCBridgeable.swift

protocol AutoObjectiveCBridgeable: _ObjectiveCBridgeable where _ObjectiveCType == ObjcType {
    associatedtype ObjcType
    
    func toObjectiveC() -> ObjcType
    static func fromObjectiveC(_ instance: ObjcType) -> Self
}

extension AutoObjectiveCBridgeable {
    // MARK: - _ObjectiveCBridgeable
    func _bridgeToObjectiveC() -> ObjcType {
        return toObjectiveC()
    }
    
    static func _forceBridgeFromObjectiveC(_ source: ObjcType, result: inout Self?) {
        if !_conditionallyBridgeFromObjectiveC(source, result: &result) {
            fatalError("Unable to bridge \(ObjcType.self) to \(self)")
        }
    }
    
    static func _conditionallyBridgeFromObjectiveC(_ source: ObjcType, result: inout Self?) -> Bool {
        result = Self.fromObjectiveC(source)
        return true
    }
    
    static func _unconditionallyBridgeFromObjectiveC(_ source: ObjcType?) -> Self {
        var result: Self?
        _forceBridgeFromObjectiveC(source!, result: &result)
        return result!
    }
}

Example.swift

struct Foo: AutoObjectiveCBridgeable {
    let value: Int
    
    func toObjectiveC() -> NSFoo {
        return NSFoo(value: value)
    }
    static func fromObjectiveC(_ instance: NSFoo) -> Foo {
        return Foo(value: instance.value)
    }
}

class NSFoo: NSObject {
    let value: NSInteger
    
    init(value: NSInteger) {
        self.value = value
    }
}

let a = Foo(value: 42)
a.value // 42
(a as NSFoo).value // 42