📦 Installation

dotnet add package Cirreum.Result

🧱 Target Frameworks

Result is built for modern, high-performance .NET, with first-class support for:

🚀 Quick Start

Basic Success / Failure

Result SaveUser(User user)
{
    if (user is null)
        return Result.Fail(new ArgumentNullException(nameof(user)));

    return Result.Success;
}

Result<User> CreateUser(string name)
{
    if (string.IsNullOrWhiteSpace(name))
        return Result<User>.Fail(new ArgumentException("Name is required"));

    return Result<User>.Success(new User(name));
}

🔗 Chaining With Then and Map

var result =
    CreateUser("Alice")
        .Map(user => user.Id)
        .Then(LogCreation);

🏭 Static Factory Methods

The non-generic Result class provides convenient factory methods:

// Create a successful Result<T>
var success = Result.From(42);  // Result<int>

// Create a failed Result<T>
var failure = Result.Fail<string>(new InvalidOperationException("Error"));

// Convert Optional<T> to Result<T>
var optional = Optional<User>.From(user);

// With direct exception
var result1 = Result.FromOptional(optional, new NotFoundException("User not found"));

// With error message (creates InvalidOperationException)
var result2 = Result.FromOptional(optional, "User not found");

// With error factory for lazy evaluation
var result3 = Result.FromOptional(optional, () => new NotFoundException($"User {id} not found"));

🎯 Optional Values

Use Optional<T> when a value may be absent without implying an error:

Creating Optionals

// When you know the value is not null
var name = Optional<string>.For("John");

// When the value might be null (null-safe)
var user = _db.Users.Find(id);
var userOptional = Optional.From(user);  // Returns Empty if null

// Explicit empty
var empty = Optional<int>.Empty;

Using Optionals

Optional<User> FindUser(int id)
{
    var user = _db.Users.Find(id);
    return Optional.From(user);  // Returns Empty if null
}

// Chaining
var displayName = FindUser(id)
    .Map(u => u.DisplayName)
    .GetValueOrDefault("Unknown");

// Pattern matching
FindUser(id).Switch(
    onValue: user => Console.WriteLine($"Found: {user.Name}"),
    onEmpty: () => Console.WriteLine("User not found"));

// Convert to Result when absence is an error
var result = FindUser(id)
    .ToResult(new NotFoundException("User not found"));

// Or use the static factory method
var result2 = Result.FromOptional(FindUser(id), new NotFoundException("User not found"));

When to Use Optional<T> vs Result<T>

📄 Pagination Results

Three result types provide consistent contracts for paginated data across any persistence implementation (SQL, NoSQL, APIs, etc.):

SliceResult<T>

The simplest pagination type—just items and a "has more" indicator. Ideal for "load more" buttons or batch processing.

// Creating a slice
var slice = new SliceResult<Order>(orders, hasMore: true);

// Empty slice
var empty = SliceResult<Order>.Empty;

// Transform items while preserving metadata
var dtos = slice.Map(order => new OrderDto(order));

// Check state
if (slice.IsEmpty) { /* handle empty */ }
if (slice.HasMore) { /* show "Load More" button */ }

CursorResult<T>

Cursor-based (keyset) pagination for stable results across data changes. Ideal for infinite scroll, real-time data, and large datasets.

// Creating a cursor result
var result = new CursorResult<Order>(orders, nextCursor: "abc123", hasNextPage: true) {
    PreviousCursor = "xyz789",
    TotalCount = 1000  // Optional
};

// Empty result
var empty = CursorResult<Order>.Empty;

// Transform items
var dtos = result.Map(order => new OrderDto(order));

// Navigation
if (result.HasNextPage) { /* use result.NextCursor */ }
if (result.HasPreviousPage) { /* use result.PreviousCursor */ }

PagedResult<T>

Offset-based pagination with full metadata. Ideal for traditional paged UIs with page numbers.

// Creating a paged result
var result = new PagedResult<Order>(orders, totalCount: 100, pageSize: 25, pageNumber: 1);

// Empty result with custom page size
var empty = PagedResult<Order>.Empty(pageSize: 50);

// Transform items
var dtos = result.Map(order => new OrderDto(order));

// Navigation and metadata
Console.WriteLine($"Page {result.PageNumber} of {result.TotalPages}");
Console.WriteLine($"Showing {result.Count} of {result.TotalCount} items");
if (result.HasNextPage) { /* show next button */ }
if (result.HasPreviousPage) { /* show previous button */ }

When to Use Each Pagination Type

Transforming Results Across Layers

All pagination types support Map() for clean DTO projections:

// Repository returns domain entities
public async Task<PagedResult<Order>> GetOrdersAsync(int page, int pageSize)
{
    // ... query implementation
}

// Service transforms to DTOs
public async Task<PagedResult<OrderDto>> GetOrderDtosAsync(int page, int pageSize)
{
    var orders = await _repository.GetOrdersAsync(page, pageSize);
    return orders.Map(order => new OrderDto(order));
}

// Controller returns the result directly
[HttpGet]
public async Task<PagedResult<OrderDto>> GetOrders(int page = 1, int pageSize = 25)
{
    return await _orderService.GetOrderDtosAsync(page, pageSize);
}

✅ Validation With Ensure

The Ensure method provides a fluent way to add validation to your Result<T> pipeline. If the predicate returns false, the success result is converted to a failure.

Synchronous Ensure

// With error message (creates InvalidOperationException)
var result = GetOrder(id)
    .Ensure(o => o.Amount > 0, "Amount must be positive");

// With exception factory for custom error types
var result = GetOrder(id)
    .Ensure(o => o.Amount > 0, o => new ValidationException($"Order {o.Id} has invalid amount: {o.Amount}"));

// With direct exception
var result = GetOrder(id)
    .Ensure(o => o.Amount > 0, new ValidationException("Amount must be positive"));

// Chain multiple validations - stops on first failure
var result = GetOrder(id)
    .Ensure(o => o.Amount > 0, "Amount must be positive")
    .Ensure(o => o.Items.Any(), "Order must have items")
    .Ensure(o => o.CustomerId != null, o => new InvalidOperationException($"Order {o.Id} has no customer"));

Async Ensure

// Async predicate with error factory
var result = await GetOrderAsync(id)
    .EnsureAsync(async o => await IsValidCustomer(o.CustomerId), 
                 o => new ValidationException($"Invalid customer: {o.CustomerId}"));

// Async predicate with direct exception
var result = await GetOrderAsync(id)
    .EnsureAsync(async o => await HasSufficientStock(o.Items), 
                 new InsufficientStockException());

// Mix sync and async validations
var result = await GetOrderAsync(id)
    .EnsureAsync(o => o.Amount > 0, "Amount must be positive")  // sync predicate
    .EnsureAsync(async o => await IsValidCustomer(o.CustomerId), "Invalid customer")  // async predicate
    .EnsureAsync(o => o.Items.All(i => i.Quantity > 0), "All items must have positive quantity");

👀 Side‑Effects With Inspect

result
    .Inspect(r => logger.LogInformation("Result: {State}", r.IsSuccess ? "OK" : "FAIL"));

⚡ Async Support (ValueTask + Task)

Every operation has async variants:

var result =
    await GetUserAsync(id)
        .OnSuccessAsync(user => logger.LogInformation("Loaded {Id}", user.Id))
        .OnFailureAsync(ex => logger.LogError(ex, "Failed to load user"));

Or with async lambdas:

await SaveAsync(entity)
    .OnSuccessTryAsync(async () => await NotifyAsync(entity));

🧩 Pattern Matching

var message = result.Match(
    onSuccess: () => "OK",
    onFailure: ex => $"Error: {ex.Message}");

🏗️ API Overview

Result (non-generic)

• IsSuccess, IsFailure, Error
• OnSuccess, OnFailure, Inspect, TryGetError
• Map, Then, Match
• Static factories:
  • From<T>(T value) - creates Result<T>
  • Fail<T>(Exception error) - creates failed Result<T>
  • FromOptional<T>(Optional<T>, Exception/string/Func<Exception>) - converts Optional<T> to Result<T>
• Async: OnSuccessAsync, OnFailureAsync, SwitchAsync, etc.

Result<T>

All of the above, plus:

• Value / TryGetValue
• Map<TOut>(...)
• Ensure(...) validation helpers:
  • Ensure(Func<T, bool> predicate, string errorMessage)
  • Ensure(Func<T, bool> predicate, Exception error)
  • Ensure(Func<T, bool> predicate, Func<T, Exception> errorFactory)

Optional<T>

• HasValue, IsEmpty, Value, TryGetValue
• For(T non-null) - creates Optional from non-null value
• Empty - static property for empty optional
• Map, Then, Match, Switch, Where
• GetValueOrDefault(T), GetValueOrDefault(Func<T>), GetValueOrNull()
• ToResult(Exception) for converting to Result<T>

Optional (non-generic factory)

• From<T>(T?) - null-safe factory method

SliceResult<T>

• Items, HasMore, Count, IsEmpty
• Empty - static property for empty slice
• Map<TResult>(Func<T, TResult>) - transform items preserving metadata

CursorResult<T>

• Items, NextCursor, HasNextPage, Count, IsEmpty
• PreviousCursor, HasPreviousPage - bidirectional navigation
• TotalCount - optional total count
• Empty - static property for empty result
• Map<TResult>(Func<T, TResult>) - transform items preserving metadata

PagedResult<T>

• Items, TotalCount, PageSize, PageNumber, Count, IsEmpty
• TotalPages, HasNextPage, HasPreviousPage - computed properties
• Empty(int pageSize = 25) - static factory for empty result
• Map<TResult>(Func<T, TResult>) - transform items preserving metadata

Async Extensions

(From ResultAsyncExtensions) Supports async versions of:

• OnSuccess
• OnSuccessTry
• OnFailure
• OnFailureTry
• Inspect
• Ensure
• Map
• Then
• Match

All support both ValueTask and Task.

🧪 Example: End‑to‑End Pipeline

var result =
    await Validate(request)
        .Then(() => LoadUser(request.UserId))
        .Ensure(u => u.IsActive, "User must be active")
        .Map(user => user.Profile)
        .OnSuccessAsync(profile => Cache(profile))
        .OnFailureAsync(ex => LogFailure(ex));

No exceptions. No branches. Pure railway flow.

📚 Real-World Examples

User Registration with Validation

public async Task<Result<User>> RegisterUserAsync(RegistrationRequest request)
{
    return await Result<RegistrationRequest>.Success(request)
        .Ensure(r => !string.IsNullOrWhiteSpace(r.Email), "Email is required")
        .Ensure(r => IsValidEmail(r.Email), "Invalid email format")
        .Ensure(r => r.Password.Length >= 8, "Password must be at least 8 characters")
        .EnsureAsync(async r => !await UserExists(r.Email), 
                     r => new DuplicateUserException($"User with email {r.Email} already exists"))
        .Map(r => new User { Email = r.Email, PasswordHash = HashPassword(r.Password) })
        .ThenAsync(async user => await SaveUserAsync(user))
        .OnSuccessAsync(async user => await SendWelcomeEmailAsync(user.Email))
        .InspectAsync(result => 
            _logger.LogInformation("Registration attempt for {Email}: {Success}", 
                request.Email, result.IsSuccess));
}

Order Processing with Stock Validation

public async Task<Result<Order>> ProcessOrderAsync(OrderRequest request)
{
    return await LoadCustomerAsync(request.CustomerId)
        .Ensure(c => c.IsActive, c => new InactiveCustomerException($"Customer {c.Id} is inactive"))
        .Ensure(c => !c.HasOutstandingBalance, "Customer has outstanding balance")
        .Map(customer => CreateOrder(customer, request.Items))
        .EnsureAsync(async order => await CheckInventoryAsync(order.Items),
                     "Insufficient inventory for one or more items")
        .Ensure(order => order.Total >= 10m, "Minimum order amount is $10")
        .ThenAsync(async order => await SaveOrderAsync(order))
        .OnSuccessAsync(async order => {
            await ReserveInventoryAsync(order.Items);
            await NotifyWarehouseAsync(order);
        })
        .OnFailureAsync(async error => {
            await _logger.LogErrorAsync(error, "Order processing failed");
            if (error is InsufficientInventoryException)
                await NotifyInventoryTeamAsync(request);
        });
}

API Response Handling with Optional

public async Task<Result<UserProfile>> GetUserProfileAsync(int userId)
{
    // Find user returns Optional<User>
    var userOptional = await _repository.FindUserAsync(userId);
    
    return userOptional
        .ToResult(new NotFoundException($"User {userId} not found"))
        .EnsureAsync(async u => await IsAuthorizedToViewProfile(u),
                     new UnauthorizedException("Not authorized to view this profile"))
        .ThenAsync(async user => {
            var profile = await LoadProfileAsync(user.Id);
            var preferences = await LoadPreferencesAsync(user.Id);
            return BuildCompleteProfile(user, profile, preferences);
        });
}

// Alternative using static factory
public async Task<Result<Product>> GetProductAsync(string sku)
{
    var productOptional = await _cache.GetProductAsync(sku);
    
    // Convert optional to result using factory method
    return Result.FromOptional(productOptional, () => new ProductNotFoundException($"Product {sku} not found"))
        .Ensure(p => p.IsAvailable, "Product is not available")
        .Ensure(p => p.Stock > 0, p => new OutOfStockException($"Product {p.Name} is out of stock"))
        .Map(p => ApplyCurrentPricing(p));
}

Paginated API with DTO Transformation

public async Task<PagedResult<OrderSummaryDto>> GetOrdersAsync(
    Guid customerId,
    int pageNumber = 1,
    int pageSize = 25)
{
    var orders = await _repository.GetOrdersByCustomerAsync(customerId, pageNumber, pageSize);
    
    return orders.Map(order => new OrderSummaryDto {
        Id = order.Id,
        OrderDate = order.CreatedAt,
        Total = order.Total,
        Status = order.Status.ToString(),
        ItemCount = order.Items.Count
    });
}

// Cursor-based for infinite scroll
public async Task<CursorResult<ActivityDto>> GetActivityFeedAsync(
    Guid userId,
    string? cursor = null,
    int pageSize = 50)
{
    var activities = await _repository.GetActivitiesAsync(userId, cursor, pageSize);
    
    return activities.Map(activity => new ActivityDto {
        Id = activity.Id,
        Type = activity.Type,
        Description = activity.Description,
        Timestamp = activity.CreatedAt
    });
}

💡 Best Practices

1. Use Specific Exception Types

// Good - specific exception with context
.Ensure(order => order.Items.Any(), 
        order => new EmptyOrderException($"Order {order.Id} has no items"))

// Less ideal - generic exception
.Ensure(order => order.Items.Any(), "Order has no items")

2. Chain Validations from General to Specific

// Good - fails fast on basic validation
result
    .Ensure(x => x != null, "Value cannot be null")
    .Ensure(x => x.Length > 0, "Value cannot be empty")
    .Ensure(x => x.Length <= 100, "Value too long")
    .EnsureAsync(async x => await IsUniqueAsync(x), "Value must be unique");

3. Use Optional<T> for Lookups, Result<T> for Operations

// Good
Optional<User> FindUserByEmail(string email);
Result<User> CreateUser(CreateUserRequest request);

// Avoid
Result<User> FindUserByEmail(string email); // Finding nothing isn't an error
Optional<User> CreateUser(CreateUserRequest request); // Creation can fail

4. Keep Async and Sync Separate

// Good - clear async boundaries
var result = ProcessSync()
    .Then(x => TransformSync(x))
    .ThenAsync(async x => await SaveAsync(x))
    .OnSuccessAsync(async x => await NotifyAsync(x));

// Avoid - mixing unnecessarily
var result = await ProcessSync()
    .ThenAsync(async x => TransformSync(x)) // Wrapping sync in async

5. Use Error Context in Factories

// Good - provides context
.Ensure(u => u.Age >= 18, 
        u => new ValidationException($"User {u.Id} is underage: {u.Age}"))

// Less helpful
.Ensure(u => u.Age >= 18, new ValidationException("User is underage"))

6. Choose the Right Pagination Type

// Good - cursor for real-time feed
public Task<CursorResult<Post>> GetTimelineAsync(string? cursor);

// Good - paged for admin dashboard
public Task<PagedResult<User>> GetUsersAsync(int page, int pageSize);

// Good - slice for "show more" preview
public Task<SliceResult<Comment>> GetRecentCommentsAsync(int limit);

// Avoid - offset pagination for large real-time data
public Task<PagedResult<Post>> GetTimelineAsync(int page); // Results shift as new posts arrive

🛠️ Why Struct‑Based?

• Avoids heap allocations
• No capturing of closures on success path
• More predictable performance in hot loops
• Perfect for high‑volume messaging, pipelines, middleware, and game engines

📜 License

This project is licensed under the MIT License.

🤝 Contributing

Pull requests are welcome! If you have ideas for improvements—performance tweaks, new helpers, analyzers—feel free to open an issue or contribute directly.

🧭 Project Files

• Core interfaces: IResult, IResult<T>
• Implementations: Result, Result<T>, Optional<T>
• Pagination: SliceResult<T>, CursorResult<T>, PagedResult<T>
• Async pipeline operators: ResultAsyncExtensions
• Monadic composition, validation, and inspection APIs
• Designed to support any .NET hosting model (Server, WASM, Azure Functions)

Made with ❤️ for clean, predictable, exception‑free flow control.

Cirreum Foundation Framework
Layered simplicity for modern .NET