Error model

ErrorType

An enum that categorises errors.

Member	Use case
Failure	Default / generic failure.
Validation	Input or state failed validation.
NotFound	A requested resource does not exist.
Conflict	Duplicate, concurrency violation, or state conflict.
Unauthorized	Missing or invalid authentication.
Forbidden	Authenticated but insufficient permissions.
Unexpected	Unhandled or unexpected scenario.

Error

A record with three positional properties and optional metadata.

public record Error(string Code, string Message, ErrorType Type = ErrorType.Failure)

Property	Type	Description
Code	string	Machine-readable identifier, e.g. "user.not_found".
Message	string	Human-readable description.
Type	ErrorType	Category. Defaults to Failure.
Metadata	IReadOnlyDictionary<string, object?>?	Optional key-value data. Set via with expressions.

Factory methods

Each ErrorType has a corresponding static factory:

Error.Failure("op.failed", "Something went wrong.");
Error.Validation("email.invalid", "Email format is invalid.");
Error.NotFound("order.not_found", "Order does not exist.");
Error.Conflict("user.duplicate", "A user with that email already exists.");
Error.Unauthorized("auth.missing", "No credentials provided.");
Error.Forbidden("auth.denied", "You do not have access.");
Error.Unexpected("unhandled", "An unexpected error occurred.");

Metadata

Attach arbitrary data using with:

var error = Error.Validation("field.required", "Name is required.")
    with { Metadata = new Dictionary<string, object?> { ["field"] = "name" } };