NancyFx VS AutoMapper

Nancyfx - sadly dead in the water now but well worth a read of both the code and docs https://github.com/NancyFx/Nancy/tree/master/

2-3 years ago Nancy added a large banner at the top of https://github.com/NancyFx/Nancy -

Being open source doesn't change the support model. It allows willing contributors to step up and fork in the event of total abandonment. As a comparison, nobody forked NancyFx to extend support or keep it alive.

It sounds like you are talking about asp.net? If you don't want to bother with controllers and attributes and all that you can just use the Microsoft.AspNetCore.Http and Microsoft.AspNetCore.Routing namespaces. As someone that really liked Nancy I felt that this was close enough.

AutoMapper

The 13.0 Upgrade Guide page was created back in April, but there is no sign of the release yet.

The most well-know is probably AutoMapper, but it's not universally liked.

AutoMapper - well for automapping

When working with AutoMapper, we often bump into runtime errors due to invalid mapping configuration, such as this one:

What problems will resolve automapper?

If you are a fan of data mappers, you might want to enhance the implementation with additional extension methods. Here is an example for AutoMapper.

I'm wondering myself. Most mappers like https://automapper.org/ will make a best effort mapper automatically via introspection. If this is just a DSL/annotation suite that requires explicit, complete mapping implementations then this strikes me as a re-implementation of parts of kotlin in kotlin.