TryExceptionHandling.cs

using System;
using System.Linq;
using System.Net;
using System.Threading.Tasks;

namespace FuncSharp.Examples;

public enum NetworkOperationError
{
    ServerError,
    ConnectionTimedOut,
    NetworkIssues
}

public static class Api
{
    public static Try<int, NetworkOperationError> GetNumber()
    {
        // This method serves as an example use-case for handling value of ITries, instead of random next, there should be some network call.
        return PerformNetworkOperation(_ => new Random().Next());
    }

    public static Try<int, NetworkOperationError> DoubleNumber(int value)
    {
        // This method serves as an example use-case for handling value of ITries, instead of multiplication, there should be some network call.
        return PerformNetworkOperation(_ => value * 2);
    }

    private static Try<T, NetworkOperationError> PerformNetworkOperation<T>(Func<Unit, T> operation)
    {
        var connectionErrorStatuses = new[]
        {
            WebExceptionStatus.ConnectFailure,
            WebExceptionStatus.ConnectionClosed,
            WebExceptionStatus.SecureChannelFailure,
            WebExceptionStatus.NameResolutionFailure
        };

        try
        {
            return Try.Success<T, NetworkOperationError>(operation(Unit.Value));
        }
        catch (TaskCanceledException)
        {
            return Try.Error<T, NetworkOperationError>(NetworkOperationError.ConnectionTimedOut);
        }
        catch (WebException e) when (e.Response.As<HttpWebResponse>().Map(r => (int)r.StatusCode > 500 && (int)r.StatusCode < 599).GetOrFalse())
        {
            return Try.Error<T, NetworkOperationError>(NetworkOperationError.ServerError);
        }
        catch (WebException e) when (connectionErrorStatuses.Contains(e.Status))
        {
            return Try.Error<T, NetworkOperationError>(NetworkOperationError.NetworkIssues);
        }
        // Notice that general Exception is not handled. We're handling the exceptions we expect, so the signature makes sense.
        // The purpose of Try is not covering every exception. But that methods should show what are the expected outputs and make the call site handle all of them.
    }
}