iOS: Storing data in memory rather than on disk

I'm looking for a tutorial on how to store sensitive data in memory rather than on disk for iOS (10+). I've googled but nothing really relevant has come up.

I'm familiar with most data storage options for iOS, SQLite, Plist, Core Data, User Defaults and Keychain. I know Core Data has an in-memory persistent store option but am not sure how to designate that as the one I want to use. Looking at the Apple docs and other tutorials I've only seen the instantiation of a persistent store but not declaring whether it was to be sqlite or core data or in-memory.

For example, Apple's docs on the Core Data stack:

import UIKit
import CoreData
class DataController: NSObject {
    var managedObjectContext: NSManagedObjectContext
    init(completionClosure: @escaping () -> ()) {
        persistentContainer = NSPersistentContainer(name: "DataModel")
        persistentContainer.loadPersistentStores() { (description, error) in
            if let error = error {
                fatalError("Failed to load Core Data stack: \(error)")
            }
            completionClosure()
        }
    }
}

This question seems to point in the right direction (just the code initially posted)

Save In-Memory store to a file on iOS

- (NSPersistentStore *)addPersistentStoreWithType:(NSString *)storeType configuration:(NSString *)configuration URL:(NSURL *)storeURL options:(NSDictionary *)options error:(NSError **)error;

Is it just that, passing a type? And to follow-up, once the app closes, the in-memory data is released?

Thanks

Since you're using NSPersistentContainer, you tell Core Data what kind of store to use with an instance of NSPersistentStoreDescription. It has a property called type that accepts values like NSInMemoryStoreType. Set up a description and then assign that to the container's persistentStoreDescriptions property, and you'll get an in-memory store. The method you mention would work but would require changing your Core Data setup to drop NSPersistentContainer.

It exists, as the name implies, only in memory, so anything stored there disappears when the app exits.