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Haitch

Overview

Haitch.Unions provides Result<T> and Optional<T> union types for representing operation outcomes and optional values without exceptions or null checks. It includes a typed Error hierarchy, fluent sync and async pipelines, ASP.NET Core integration, and TUnit assertions.

Targets .NET 10+.

Installation

Section titled “Installation”
Terminal window
dotnet add package Haitch.Unions
dotnet add package Haitch.Unions.AspNetCore        # optional: Result -> HTTP results and ProblemDetails
dotnet add package Haitch.Unions.TUnit.Assertions  # optional: TUnit assertions

Quick example

Section titled “Quick example”
using Haitch.Unions;


Result<User> GetUser(int id) =>
    repository.Find(id) is { } user
        ? user
        : new NotFoundError("User.NotFound", $"User {id} not found");


var name = GetUser(42)
    .Ensure(user => user.IsActive, new ValidationError("User.Inactive", "User is inactive"))
    .Map(user => user.DisplayName)
    .Match(
        onOk: displayName => displayName,
        onError: _ => "Anonymous");

Core concepts

Section titled “Core concepts”

Result<T> represents an operation that is either Ok, holding a T, or Error, holding an Error. There is no non-generic Result type — an operation with nothing to return uses Result<Unit>.

Optional<T> represents a value that may or may not be present: Some holding a T, or None.

Error is the base of a typed hierarchy — NotFoundError, ValidationError, ConflictError, UnauthorizedError, ForbiddenError, and UnexpectedError — instead of a single record with an enum tag.

Both Result<T> and Optional<T> are C# unions ([Union]/IUnion), so switch expressions work alongside Match — see Pattern matching.

Implicit conversions

Section titled “Implicit conversions”

Both Result<T> and Optional<T> support implicit conversion, so you can return values or errors directly without calling factory methods.

Result<User> GetUser(int id)
{
    var user = db.Find(id);
    if (user is null)
        return new NotFoundError("user.not_found", $"No user with id {id}.");


    return user; // implicit Ok
}


Optional<string> GetNickname(User user) => user.Nickname; // null becomes None