Escaped Continuation

EscapedContinuation.swift

///
/// # EscapedContinuation
///
/// ## Usage
///
/// 1. Call:
///
/// ```swift
/// let continuation = await EscapedContinuation<ReturnsType>()
/// ```
///
/// 2. Then, call either
/// ```swift
/// await continuation.onSuccess(_ value: ReturnsType)
/// await continuation.onError(_ error: any Error)
/// ```
/// somewhere else in your code (you can wrap it in a `Task` if neccessary).
/// > Note: The continuation must be resumed only once.
///
/// 3. Finally, return the result:
/// ```swift
/// return try await continuation.task.value
/// ```
///

actor EscapedContinuation<ReturnsType> {
        
    var task: Task<ReturnsType, any Error>!
    
    private var continuation: CheckedContinuation<ReturnsType, any Error>!
    
    /// The continuation must be resumed exactly once.
    private var didResume = false
    
    
    func onSuccess(_ value: ReturnsType) {
    
        guard !didResume else {
            return
        }
        
        didResume = true
        
        continuation.resume(returning: value)
        
    }
    
    func onError(_ error: any Error) {
        
        guard !didResume else {
            return
        }
        
        didResume = true
        
        continuation.resume(throwing: error)
        
    }
    
    
    init() async {
                
        task = Task {
            
            return try await withCheckedThrowingContinuation { continuation in
                
                self.continuation = continuation
                
            }
            
        }
        
    }
    
}