v3.x to v4.x

This page describes a historical upgrade. Its replacement code was correct for 4.x, and later majors have removed some of the API it names — UseExceptionLogger, ErrorCode.FromEnum and the ErrorCodeFactory.FromEnum override are all gone in 7.0.0. UseErrorCodeFactory itself remains, but it can no longer shape enum codes. Land on 4.x first if you are following these steps, then read the pages in order. Deprecations lists what has gone since.

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Pointed at your solution, in Claude Code or a similar tool.

Upgrade this solution from Waystone.Monads v3 to v4. Report what you changed.

1. Replace every MonadsGlobalConfig call with MonadOptions.Configure. The Use* methods
   move inside the callback, and FallbackErrorCode and FallbackErrorMessage are set as
   properties on the options object.

2. Find every implementation of IErrorCodeFormatter<T>. That interface is gone. Convert
   each to a class deriving from ErrorCodeFactory, and register it once at start-up with
   MonadOptions.Configure(options => options.UseErrorCodeFactory(new MyFactory())).

3. Delete the formatter argument from every ErrorCode.FromEnum call. The factory is
   applied for the life of the application now, not per call.

4. Build and report anything left. Do not suppress a diagnostic to make it go away.

Replaced MonadsGlobalConfig with MonadOptions to enable better DX when configuring library behaviours.

-MonadsGlobalCongig.UseExceptionLogger(...);
+MonadOptions.Configure(options => {
+    options.UseExceptionLogger(...)
+           .UseErrorCodeFactory(...)
+    options.FallbackErrorCode = "error.unknown";
+    options.FallbackErrorMessage = "An unknown error has occurred.";
+});

The IErrorCodeFormatter<T> interface has been removed in favour of ErrorCodeFactory so that it can be applied once during your app's life-cycle, instead of during each invocation of the error code creation methods. You can override the default formatting by inheriting ErrorCodeFactory and invoking MonadOptions.UseErrorCodeFactory().

-class MyErrorCodeFormatter<MyErrorCodeEnum> : IErrorCodeFormatter<MyErrorCodeEnum>;
-ErrorCode.FromEnum(MyErrorCodeEnum.BadRequest, new MyErrorCodeFormatter<MyErrorCodeEnum>());
+class MyErrorCodeFactory : ErrorCodeFactory;
+MonadOptions.Configure(options => options.UseErrorCodeFactory(new MyErrorCodeFactory()));