The problem with async load/subscribe

[tevelee]

Pointfree episode #310 provided a somewhat unclear explanation regarding the current requirement for SharedReaderKey, which includes:

func load(context: LoadContext<Value>, continuation: LoadContinuation<Value>)

rather than:

func load(context: LoadContext<Value>) async throws

Additionally, the subscribe method does not utilize TaskGroup return AsnycSequence.

I am curious to understand the technical challenges involved in implementing this.

[mbrandonw]

Hi @tevelee, it simply wreaks havoc on testing. You would not even be able to do something as simple as:

@Test func basics() {
  UserDefaults.standard.set(42, forKey: "count")
  @Shared(.appStorage("count")) var count = 0
  #expect(count == 42)  // ❌ Expected 42, actual 0.
}

…because load is async. You would need to insert Task.sleep around every usage of the shared value.

Additionally, the subscribe method does not utilize TaskGroup.

FWIW, that is not the shape subscribe would have. It would instead need to return an any AsyncSequence.