Dynamic member lookup based simplification to access nested dictionary fields

JSONContainer.swift

@dynamicMemberLookup
final class JSONContainer {
    private typealias Dict = [String: Any]
    
    private enum Container {
        case dict(Dict), value(Any), nothing
    }
    
    private let _container: Container
    init(_ dict: [String: Any]) {
        _container = .dict(dict)
    }
    
    init(_ value: Any) {
        _container = (value as? Dict).map(Container.dict) ?? .value(value)
    }
    
    private init() {
        _container = .nothing
    }
    
    /// Get either dictionary value by field name, or array value by index
    subscript(dynamicMember member: String) -> JSONContainer {
        switch _container {
        case .dict(let dict):
            if let value = dict[member] {
                return JSONContainer(value)
            }
        case .value(let arr as [Any]):
            if let index = Int(member), arr.indices.contains(index) {
                return JSONContainer(arr[index])
            }
        default:
            break
        }
        return JSONContainer()
    }
    
    /// Cast to type
    func `as`<T>(_ type: T.Type) -> T? {
        switch _container {
        case .value(let value as T), .dict(let value as T):
            return value
        default:
            return nil
        }
    }
    
    /// Substitute to reciever type
    func sub<T>() -> T? {
        return `as`(T.self)
    }
}

extension Dictionary where Key: CustomStringConvertible {
    var json: JSONContainer {
        return JSONContainer(self)
    }
}

let fifthNumber = dict.json.phone_numbers.4.number.as(String.self)
let categoryName: String? = dict.json.type.category.name.sub()