Trellis.Results 3.0.0-alpha.127

Railway Oriented Programming

Composable error handling for .NET using Result<T>, Maybe<T>, and 10 discriminated error types. No exceptions, no null — just clean pipelines that read like English.

Installation

dotnet add package Trellis.Results

Quick Start

using Trellis;

// Chain operations — errors short-circuit automatically
Result<string> result = GetUser(userId)
    .Ensure(user => user.IsActive, Error.Validation("User is not active"))
    .Tap(user => _logger.LogInformation("Accessed {Id}", user.Id))
    .Map(user => user.Email);

// Pattern match the result
result.Match(
    onSuccess: email => Console.WriteLine($"Email: {email}"),
    onFailure: error => Console.WriteLine($"Error: {error.Detail}")
);

Core Types

Result<T>

Represents success (with a value) or failure (with an error).

Result<int> success = 42;                                    // Implicit conversion
Result<int> failure = Error.NotFound("Item not found");      // Implicit conversion

if (success.IsSuccess)
    Console.WriteLine(success.Value);  // 42

Maybe<T>

Domain-level optionality — replaces nullable references.

Maybe<string> some = Maybe.From("hello");
Maybe<string> none = Maybe.None<string>();

string greeting = some.Match(
    s => $"Hi, {s}!",
    () => "No name");

Error Types

Pipeline Operations

All operations have async variants (BindAsync, MapAsync, etc.) with CancellationToken support. LINQ query syntax is also supported (from, select, where) for both Result<T> and Maybe<T>.

Real-World Example

public Result<Order> PlaceOrder(OrderRequest request)
{
    return ProductId.TryCreate(request.ProductId)
        .Combine(Quantity.TryCreate(request.Quantity))
        .Bind((productId, qty) => _inventory.Reserve(productId, qty))
        .Ensure(reservation => reservation.IsConfirmed, 
            Error.Conflict("Item is out of stock"))
        .Map(reservation => Order.FromReservation(reservation))
        .Tap(order => _events.Publish(new OrderPlaced(order.Id)));
}

Combine — Collect All Errors

// Validates ALL fields and returns ALL errors at once
var result = FirstName.TryCreate(input.FirstName)
    .Combine(LastName.TryCreate(input.LastName))
    .Combine(EmailAddress.TryCreate(input.Email))
    .Bind((first, last, email) => User.TryCreate(first, last, email));

Performance

11–16 nanoseconds per operation — 0.002% of a typical database query. Zero extra allocations on Combine.

Related Packages

• Trellis.Primitives — Type-safe value objects (EmailAddress, Money, etc.)
• Trellis.DomainDrivenDesign — Aggregate, Entity, ValueObject
• Trellis.Asp — ASP.NET Core integration (Result → HTTP responses)
• Trellis.Http — HttpClient → Result<T> extensions
• Trellis.Analyzers — 19 Roslyn analyzers enforcing ROP best practices
• Trellis.Testing — FluentAssertions extensions for Result<T>

License

MIT — see LICENSE for details.