How to call async methods in an Array map or forEach? - swift

Question

I'm making my first attempts with Swift's async/await features and Task.
My first goal is working with NSItemProvider. I have a custom class that extends NSObject and conforms to NSSecureCoding. I have working code that converts my class to and from NSItemProvider.
What I'm now trying to do is convert an array of NSItemProvider objects back into an array of MyClass objects. Each conversion requires a call to an async function.
I'm able to do this using a plain for in loop. The trouble begins when I try to use compactMap or forEach to create the new array from the array of NSItemProvider.
Here is some code that can be copied into a Swift Playground or project that demonstrates the issue.
import Foundation
class MyClass: NSObject, NSSecureCoding {
var name: String
override var description: String {
return name
}
init(name: String) {
self.name = name
}
static var supportsSecureCoding = true
func encode(with coder: NSCoder) {
coder.encode(name, forKey: "name")
}
required init?(coder: NSCoder) {
if let name = coder.decodeObject(of: NSString.self, forKey: "name") as? String {
self.name = name
} else {
return nil
}
}
}
extension MyClass {
static let identifier = "mySpecialId"
func asItemProvider() -> NSItemProvider {
return NSItemProvider(item: self, typeIdentifier: Self.identifier)
}
static func create(withItemProvider itemProvider: NSItemProvider) async throws -> Self? {
let res = try await itemProvider.loadItem(forTypeIdentifier: identifier)
return res as? Self
}
}
func example() {
Task {
let objs = [ MyClass(name: "A"), MyClass(name: "B"), MyClass(name: "C"), MyClass(name: "D") ]
let providers: [NSItemProvider] = objs.map { $0.asItemProvider() }
do {
// This basic `for in` loop works
var newObjs = [MyClass]()
for provider in providers {
if let obj = try await MyClass.create(withItemProvider: provider) {
newObjs.append(obj)
}
}
print("newObjs: \(newObjs)")
// Attempt to use `forEach`
// Error: Cannot pass function of type '(NSItemProvider) async -> MyClass?' to parameter expecting synchronous function type
/*
providers.forEach { provider in
if let obj = try await MyClass.create(withItemProvider: provider) {
newObjs.append(obj)
}
}
*/
// Attempt to use `compactMap`
// Error: Cannot pass function of type '(NSItemProvider) async -> MyClass?' to parameter expecting synchronous function type
//let newObjs2 = providers.compactMap { await MyClass.create(withItemProvider: $0) }
} catch {
}
}
}
I was looking at another question but the solutions are far more complicated than just using a simple for in loop.
Is there a simpler way to use compactMap, for example, to directly convert the array of NSItemProvider into an array of MyClass?