Boxing up AnyRealmCollection

AnyRealmCollectionBox.swift

// https://stackoverflow.com/questions/54764362/swift-array-of-tuples-with-generic-tuple-elements/54768030

struct AnyRealmCollectionBox<Element> {
    public func index(after i: Int) -> Int { return i + 1 }
    public func index(before i: Int) -> Int { return i - 1 }

    private let _realm: () -> Realm?
    public var realm: Realm? { return _realm() }

    private let _isInvalidated: () -> Bool
    public var isInvalidated: Bool { return _isInvalidated() }

    private let _count: () -> Int
    public var count: Int { return _count() }

    private let _description: () -> String
    public var description: String { return _description() }

    private let _indexOf: (Element) -> Int?
    public func index(of object: Element) -> Int? { return _indexOf(object) }

    private let _indexMatching: (NSPredicate) -> Int?
    public func index(matching predicate: NSPredicate) -> Int? { return _indexMatching(predicate) }

    // ...
}

extension AnyRealmCollectionBox where Element: RealmCollectionValue {
    init(_ collection: AnyRealmCollection<Element>) {
        _realm = { collection.realm }
        _isInvalidated = { collection.isInvalidated }
        _count = { collection.count }
        _description = { collection.description }
        _indexOf = { collection.index(of: $0) }
        _indexMatching = { collection.index(matching: $0) }
        //...
    }
}

struct Model<Element> {

    // 1. a String field
    let string: String

    // 2. either an Array<SomeElement>, or AnyRealmCollection<SomeObject>
    enum Container {
        case array([Element])
        case realmCollection(AnyRealmCollectionBox<Element>)
    }
    let elements: [Container]

    // 3. a closure that acts upon the specific SomeElement or SomeObject.
    let process: (Element) -> Void
}

I'm starting to write my own gists and was looking into your gists for inspiration.

The idea to link a related stackoverflow link is smart. Any other suggestions when it comes to writing gists?