RopStarterPack

Simple Railway Oriented Programming library for C#.

Rationale

Minimal by design. Just essentials. Beginner friendly. Two goals: enforce code consistency and solve error handling.

Install

dotnet add package RopStarterPack

Usage

Define your error type with factories:

using RopStarterPack; abstract record AppError { public record UserNotFound(string UserId) : AppError; public record OrderNotFound(string OrderId) : AppError; public record UnknownError(Exception Ex) : AppError; // Factories (help type inference) public static AppError UserNotFoundErr(string userId) => new UserNotFound(userId); public static AppError OrderNotFoundErr(string orderId) => new OrderNotFound(orderId); // Catch-all for unhandled exceptions public static AppError FromException(Exception ex) => new UnknownError(ex); }

Wrap external calls:

async Task<Result<Order, AppError>> GetOrderSafe(string orderId) => await Result.From( async () => { var order = await db.GetOrder(orderId); return Result.FromNullable(order, AppError.OrderNotFoundErr(orderId)); }, AppError.FromException ); async Task<Result<User, AppError>> GetUserSafe(string userId) => await Result.From( async () => { var user = await db.GetUser(userId); return Result.FromNullable(user, AppError.UserNotFoundErr(userId)); }, AppError.FromException );

Chain operations:

Task<Result<string, AppError>> ProcessOrder(string orderId) => GetOrderSafe(orderId) .AndThen(order => GetUserSafe(order.UserId)) .Map(user => $"Order belongs to {user.Name}");

Handle at the boundary:

var result = await ProcessOrder("order-123"); var response = result.Match( ok: msg => Ok(msg), err: e => e switch { AppError.UserNotFound(var id) => NotFound($"User {id} not found"), AppError.OrderNotFound(var id) => NotFound($"Order {id} not found"), AppError.UnknownError(var ex) => InternalError(ex.Message) } );

License

MIT