Class Initializer with #escaping parameter - swift

Question

I'm setting up a class that can ideally store an async method for later use. I would like to pass a function inside of class initializer but I'm running into a weird compiler issue.
Cannot convert value of type '(#escaping (Int) -> Void) -> ()' to expected argument type '((Int) -> Void) -> Void'
If the method is not escaping/sync this works fine. The compiler also suggest to force cast the parameter as! (((Int) -> Void) -> Void). Gave that a shot but it crashes.
Here's an example I've been messing with in a playground:
class NumberTwo {
let numberTwoMethod: ((Int) -> Void) -> Void
init(numberTwoMethod: #escaping ((Int) -> Void) -> Void) {
self.numberTwoMethod = numberTwoMethod
}
func callNumberTwoMethod() {
numberTwoMethod { myNum in
print(myNum)
}
}
}
func getNumberTwoMethod(completion: #escaping (Int) -> Void) {
DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
completion(2)
}
}
func getNumberTwoMethodSync(completion: (Int) -> Void) {
completion(2)
}
NumberTwo(numberTwoMethod: getNumberTwoMethod) // error: cannot convert value of type '(#escaping (Int) -> Void) -> ()' to expected argument type '((Int) -> Void) -> Void'
NumberTwo(numberTwoMethod: getNumberTwoMethodSync) // Works
Any suggestions on what's going on here or alternative ways of storing an async function as a variable in a class?

Answer 1

You are missing #escaping on the inner closure:
class NumberTwo {
let numberTwoMethod: (#escaping (Int) -> Void) -> Void
init(numberTwoMethod: #escaping (#escaping (Int) -> Void) -> Void) {
self.numberTwoMethod = numberTwoMethod
}
func callNumberTwoMethod() {
numberTwoMethod { myNum in
print(myNum)
}
}
}
or slightly simplified:
class NumberTwo {
typealias CompletionHandler = (Int) -> Void
let numberTwoMethod: (#escaping CompletionHandler) -> Void
init(numberTwoMethod: #escaping (#escaping CompletionHandler) -> Void) {
self.numberTwoMethod = numberTwoMethod
}
func callNumberTwoMethod() {
numberTwoMethod { myNum in
print(myNum)
}
}
}
Also note this will probably create a memory leak since there is no weak anywhere.