ErrorApi.CSharpFunctionalExtensions 1.0.1

ErrorApi.CSharpFunctionalExtensions

Maps CSharpFunctionalExtensions onto Minimal API results and ErrorApi's documented error catalog: every endpoint's OpenAPI document lists the failures it can actually return, and the wire response carries a stable machine-readable code — resolved at compile time by the ErrorApi source generator, with no reflection at runtime.

dotnet add package ErrorApi.CSharpFunctionalExtensions

The package brings the generator with it (PrivateAssets="none"), so referencing the adapter is the whole setup.

Before

A Result<T, E> maps to a response at runtime, in a mapper you wrote yourself — and the OpenAPI document never learns about it:

public Result<Order, OrderError> GetById(Guid id) =>
    _orders.TryGetValue(id, out var order) ? order : new OrderNotFound(id);

app.MapGet("/orders/{id:guid}", (Guid id, IOrderService s) =>
    s.GetById(id).Match(Results.Ok, e => Results.NotFound()));   // hand-rolled, per endpoint
// Document: 200 OK. The 404 exists — the frontend meets it in production.

After

Result<T, E> is the sweet spot for ErrorApi, because the failure already is a type of your own — that is exactly where the catalog entry goes:

public abstract record OrderError;

[ErrorApi.Error("Orders.NotFound", 404, Title = "Order not found")]
public sealed record OrderNotFound(Guid Id) : OrderError;

public Result<Order, OrderError> GetById(Guid id) =>
    _orders.TryGetValue(out var order) ? order : new OrderNotFound(id);

builder.Services.AddErrorApi();
app.MapGet("/orders/{id:guid}", (Guid id, IOrderService s) => s.GetById(id).ToHttpResult());
// Document: 200 + 404 with code "Orders.NotFound", title, and an example body.
// Wire:     { "title": "Order not found", "status": 404, "code": "Orders.NotFound" }

The generator documents the endpoint wherever it sees a case constructed; at runtime the instance resolves through a generated pattern switch — no reflection, native-AOT clean.

The whole surface

A string-error Result<T> resolves only when the string is a known catalog code; anything else answers as a 500 carrying the message — deliberately unhelpful as a contract, because a message is not one. Prefer Result<T, E>.

Versions

Pinned to the CSharpFunctionalExtensions version in this repository's Directory.Packages.props; the test suite also runs against older releases in CI (-p:CfeTestVersion=x.y.z).