Browse Questions
  • All three transform collections but handle the results differently.
  • Secure Message is a stateless asymmetric primitive that encrypts or signs a single payload using your private key and the peer's public key, making it a natural fit for request/response APIs.
  • A race condition occurs when two or more threads access shared mutable state simultaneously, producing unpredictable results depending on timing.
  • withCheckedContinuation bridges old callback-based APIs into the async/await world.

Answer: withCheckedContinuation bridges old callback-based APIs into the async/await world. Use it to wrap any completion-handler function so it can be awaited.

Code Example:

// Old callback-based API
func fetchData(completion: @escaping (Data?, Error?) -> Void) { ... }

// Wrap it for async/await use
func fetchData() async throws -> Data {
    try await withCheckedThrowingContinuation { continuation in
        fetchData { data, error in
            if let error = error {
                continuation.resume(throwing: error)
            } else if let data = data {
                continuation.resume(returning: data)
            }
        }
    }
}

// Now you can await it
let data = try await fetchData()

Key Rules:

  • continuation.resume() must be called exactly once — never zero, never twice
  • Use withCheckedThrowingContinuation when the operation can fail
  • withUnsafeContinuation skips the "called once" check — only use if performance is critical