Is it appropriate to mix Polly and FluentResults?

[dguisinger]

I'm looking at evaluating Polly. Since it performs error some handling to do things such as retries, would it work well in a project where a lot of error handling/propagation is already performed by FluentResults? Or would that be a bad combination and not work as intended?

[peter-csala]

Hi Dan, I have used Polly and FluentResults separately (in different projects). I don't see any fundamental problem to use both together. Result.Try might be tricky in some cases but others should work flawlessly IMHO.

If you have a particular problem that you try to solve with Polly and FluentResults then please share with us so, we can create a POC.

[dguisinger]

I'll give it a try, I think I was mainly concerned about whether or not anything would work if I used Result.Try to catch exceptions in code that is being retried.

[peter-csala]

Here I have put together an example:

public class Program
{
	public static void Main()
	{
		var retry = new ResiliencePipelineBuilder<Result<int>>()
			.AddRetry(new ()
			{
				ShouldHandle = static args => args.Outcome switch
				{
						{ Result: { IsFailed: true, Errors: List<IError> errs } } when (errs.OfType<ExceptionalError>().Any()) => PredicateResult.True(),
						_ => PredicateResult.False()
				},
				MaxRetryAttempts = 5,
				OnRetry = static args =>
				{
					 Console.WriteLine("OnRetry, Attempt: {0}", args.AttemptNumber);
					return default;
				}
			})
			.Build();
		
		var res = retry.Execute(Get);
		res.Dump();
	}
	
	private static Result<int> Get()
	{
		return Result.Try<int>(GetCore, ex => 
			Random.Shared.Next() % 2 == 0 
				? new ExceptionalError("Something went wrong", ex)
				: new CustomError("Something went terribly wrong")	
			);
	}
	
	private static int GetCore()
	{
		if(Random.Shared.Next() % 2 == 0)
		{
			throw new Exception("Not worked");
		}
		return 42;
	}	
}

public class CustomError : Error
{
    public CustomError(string message)
        : base(message)
    { 
    }
}

• GetCore either returns the meaning of life or throws an exception
• Get wraps the outcome of the GetCore into a Result<int> object
  • If GetCore returned 42 then a successful Result<int> is created
  • If GetCore threw an exception then either an ExceptionalError or a CustomError is created
• Main defines a retry strategy which should trigger
  • only if the Result is failed and contains an ExceptionalError

I know, it is a really made up example but it shows that Polly and FluentResults can work together smoothly.

[dguisinger]

Beautiful, thank you for putting that together. With no experience yet with Polly I wasn't sure if I had to let exceptions flow down. Now I see I don't, that helped a lot.