PromiseKit retrying functions using encapsulated blocks that return promises

retry.swift

/// Retries the given throwing `block` as a promise `tries` times,
/// re-calling `block` another time until exhausting the tries.
func retry<T>(tries count: Int, block: () throws -> T) -> Promise<T> {
    return Promise().thenRetry(tries: count, block: block)
}

/// Retries the given promise-returning `block` as a promise `tries` times,
/// re-calling `block` another time until exhausting the tries.
func retry<T>(tries count: Int, block: () -> Promise<T>) -> Promise<T> {
    return Promise().thenRetry(tries: count, block: block)
}

extension Promise {
    /// After succeeding this promise, re-tries the given block `tries` times, re-calling `block` another time
    /// to try to fetch another promise until exhausting the tries.
    func thenRetry<U>(tries count: Int, block: (T) throws -> Promise<U>) rethrows -> Promise<U> {
        return self.then { ret in
            return try block(ret)
        }.recover { error -> Promise<U> in
            if(count > 0) {
                return try self.thenRetry(tries: count - 1, block: block)
            }
            
            throw error
        }
    }
    
    /// After succeeding this promise, re-tries the given block `tries` times, re-calling `block` another time
    /// to try to fetch another value until exhausting the tries.
    func thenRetry<U>(tries count: Int, block: (T) throws -> U) -> Promise<U> {
        return self.then { ret in
            return try block(ret)
        }.recover { error -> Promise<U> in
            if(count > 0) {
                return self.thenRetry(tries: count - 1, block: block)
            }
            
            throw error
        }
    }
}

/*
Example:
  
  // As the start of a promise chain...
  retry(tries: 3) {
    myAsyncTask()
  }.then {
    // myAsyncTask succeeded within 3 retries!
  }.error { error in
    // myAsyncTask failed...
  }
  
  // As the continuation of a promise...
  myAsyncTask().thenRetry(tries: 3) { result in
    myOtherAsyncTask()
  }.then {
    // myOtherAsyncTask succeeded within 3 retries!
  }.error { error in
    // myAsyncTask or myOtherAsyncTask failed...
  }
*/