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import UIKit

class Debug {
    static var window: UIWindow?

    static func setupWindowIfNeeded() {
        guard Debug.window == nil else { return }
        guard Environment.current != .release else { return }

        let window = UIWindow(frame: UIScreen.main.bounds)

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// MyPrivateClass.h

@interface MyPrivateClass: NSObject

- (void) doSomethingInternalWithSecretAttribute:(NSInteger)attribute;

@end

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// Somewhere in the wild west
import MyFramework

...

// This should work
let publicClass = MyPublicClass()
publicClass.doSomethingWithPrivateClass()

...

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// MyPublicClass.swift

import MyFramework.Private // Required to see "private" header

public class MyPublicClass {
    private let privateClass: MyPrivateClass
    ...

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// Somewhere in the wild west
import MyFramework
import MyFramework.Private

...

// This should not be possible, nor even compile,
// as it should not be able to see MyPrivateClass
let privateClass = MyPrivateClass()
privateClass.doSomethingInternal(withSecretAttribute: 13)

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// ObjectiveCToSwift.swift

@objc(MyPrivateClassProtocol) // Under this name this will cross Swift->ObjC boundary
internal protocol MyPrivateClass {
    init()
    func doSomethingInternal(withSecretAttribute: Int)
}

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// SwiftToObjectiveC.h

#ifndef SwiftToObjectiveC_h
#define SwiftToObjectiveC_h

SWIFT_PROTOCOL_NAMED("MyPrivateClassProtocol")
@protocol MyPrivateClassProtocol

- (nonnull instancetype)init;
- (void)doSomethingInternalWithSecretAttribute:(NSInteger)attribute;

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// MyPrivateClass.h

#import <Foundation/Foundation.h>
#import <SwiftToObjectiveC.h>

@interface MyPrivateClass : NSObject<MyPrivateClassProtocol>

- (void) doSomethingInternalWithSecretAttribute:(NSInteger)attribute;

@end

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protocol SomeProtocol {
    init()
}
class SomeClass: SomeProtocol {
    ...
}

// This will work
let instance: SomeProtocol = SomeClass.init()

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...

@objc(Factory)
internal class Factory: NSObject {
    private static var privateClassType: MyPrivateClass.Type!

    @objc static func registerPrivateClassType(type: MyPrivateClass.Type) {
        print("REGISTRATION CALLED WITH TYPE = \(type)")
        privateClassType = type
    }