Using Result type with async/await

[Dmitriy_Ignatyev]

@gahms

guard case .success(let products) = result else {
    handleFailure(result)
    return
}

The syntax is not great now, but if you want to make async calls one by one, try this:

func doSomething() async {
  let productsResult = await fetchProducts()

  let products: [Product]
  switch productsResult {
    case .success(let success): products = success
    case .failure(let error): return await handleError(error)
  }
  
  let productImagesResult = await fetchProductImages(products)
  // ...
}

There ere some discussions about improving of syntax:

Is it possible to make early exit in do-try-catch block? (Like `guard`)

It would be convenient to have do-try-catch block in "early-exit style". Like: do-guard let encrypted = try cypher.encrypt(bytes) catch let e { print("Encryption error:", e) return // Thank Adrian for reminding } // Massive code send(encrypted) I may be wrong, but it's not implemented yet.

Precise error typing in Swift

Introduction When error handling was added to Swift in 2015, it intentionally did not allow the expression of precise error types: either a function cannot throw, or it can throw any Error. The error-handling rationale I wrote, which uses an awful lot of words to describe most aspects of the design, gives this one pretty short shrift: There are many kinds of error. It's important to be able to recognize and respond to specific error causes programmatically. Swift should support easy pattern-m…

guard-catch with typed throws can make such things easier.
Result can be easily transformed to typed throw, if these features come into play. So may be in future soothing like this can be possible:

extension Result {
  func getValueOrThrow() throws Failure -> Success {
    switch self {
    case .success(let success): return success
    case .failure(let error): throw error
    }
  }
}

func doSomething() async {
  guard let products: [Product] = await fetchProducts().getValueOrThrow() catch {
    return await handleError(error) // the error here is of concrete type, the same as in Result
  }  
  let productImagesResult = await fetchProductImages(products)
  // ...
}