Source generation

Mark an enum with [ErrorCodeCatalog] and get its error codes as compile-time constants, generated at build time.

Waystone.Monads ships a source generator inside the package. It ships from 6.2.0. You add no reference and configure nothing. It stays silent until you mark an enum with [ErrorCodeCatalog].

Which page do you want

You want to	Read
Know why this exists and turn it on	This page
Know exactly what it emits	Error code catalogs
Change the shape of the generated strings	Code format language
Review your codes, or fail a build when they drift	Reviewing generated codes
Understand a WMG build error	Generator diagnostics

Hand-written ErrorCode values are a different thing, and they are on Errors. This group covers the generated ones only.

Why it exists

Up to 6.x, ErrorCode.FromEnum(InputErrors.Missing) worked out the string "InputErrors.Missing" at run time, by reflecting over the enum. That meant the string your callers saw was not written anywhere you could point at. You could not use it in a switch, you could not put it in an attribute, and you could not find every place that read it.

Mark the enum with [ErrorCodeCatalog] and Waystone.Monads generates those strings as constants when you build.

ErrorCode.FromEnum was obsolete from 6.2.0 and 7.0.0 removes it, so this group describes the only supported way to get an error code from an enum. See Deprecations for the migration.

Marking an enum

using Waystone.Monads.Results.Errors;

namespace Ordering;

[ErrorCodeCatalog]
public enum OrderErrorCode
{
    NotFound,
    AlreadyShipped,
}

That gives you a new class next to the enum, OrderErrorCodeCatalog, in the same namespace and with the same accessibility as the enum.

The name is the enum's own name with Catalog on the end, and nothing is taken off it. OrderFailure gives you OrderFailureCatalog; OrderErrorCode gives you OrderErrorCodeCatalog. If that reads twice, rename the enum — two enums whose names differ always get two catalogs whose names differ.

Next: what the catalog contains.