What is `async let` and when is it useful?

A race condition occurs when two or more threads access shared mutable state simultaneously, producing unpredictable results depending on timing.
You can detect memory leaks automatically in unit tests by attaching an addTeardownBlock to XCTestCase with a weak reference to the system under test and asserting that the instance deallocates to…
async let starts a child task immediately and lets you await its result later.
Most candidates fail coding interviews not because they can't code, but because they lack a structured thinking process.

Answer: async let starts a child task immediately and lets you await its result later. It's the cleanest way to run a fixed number of async operations in parallel.

Code Example:

// Sequential — slow (waits for each one)
func loadDashboard() async throws -> Dashboard {
    let user = try await fetchUser()          // waits
    let posts = try await fetchPosts()        // then waits
    let notifications = try await fetchNotifications() // then waits
    return Dashboard(user: user, posts: posts, notifications: notifications)
}

// Parallel with async let — all three start at the same time
func loadDashboard() async throws -> Dashboard {
    async let user = fetchUser()
    async let posts = fetchPosts()
    async let notifications = fetchNotifications()

    return try await Dashboard(
        user: user,
        posts: posts,
        notifications: notifications
    )
}

Rule of thumb: Use async let for a fixed set of concurrent operations. Use TaskGroup for a dynamic number.