DynamicMemberLookup_Observables.swift

@dynamicMemberLookup
class Observable<T> { }

extension Observable {
	func map<Result>(_ transform: @escaping (T) -> Result) -> Observable<Result> {
		// Apply transform function here
		fatalError()
	}
	
	subscript<Property>(dynamicMember keyPath: KeyPath<T, Property>) -> Observable<Property> {
		map { $0[keyPath: keyPath] }
	}
}

struct ShoppingList {
	var items: [String] = []
}

let shoppingList = Observable<ShoppingList>()

// With Map
let mapItems = shoppingList.map { $0.items }

// With dynamicMemberLookup
let lookupItems = shoppingList.items