Swift NullableContinuation

NullableContinuation.swift

import Foundation

/// API's out of our control can sometimes callback more than once, causing the continuation to crash
/// This class is a wrapper that should avoid this crash
/// Not recommended to be used largely, but it can help if really needed to use the problematic API
public class NullableContinuation<T, E> where E : Error {
    
    private var checkedContinuation: CheckedContinuation<T,E>?
    
    public init(checkedContinuation: CheckedContinuation<T,E>) {
        self.checkedContinuation = checkedContinuation
    }
    
    public func resume(returning value: T) {
        checkedContinuation?.resume(returning: value)
        checkedContinuation = nil
    }
}

public func withNullableContinuation<T>(_ body: (NullableContinuation<T, Never>) -> Void) async -> T {
    await withCheckedContinuation { continuation in
        let nullableContinuation = NullableContinuation(checkedContinuation: continuation)
        body(nullableContinuation)
    }
}