René Meusel

> Regarding `/Zc:preprocessor`, it still builds okay, so I assume its fine without? I added that for a change in the tests. So if the unit tests (`make tests`) still...

> Are either of you anticipating me making any changes on this PR? This is awaiting approval by @randombit

Nice! @FAlbertDev and I had discussed whether the "builder pattern" would be a good fit here. And we're convinced it is! One alternative I think is worth considering besides Builder...

Also, I'd love to throw in another requirement while we're adding flexibility to these classes: Requirement: **Allow passing pre-constructed primitives (i.e. `Padding` and `HashFunction`)** I acknowledge that most users will...

I've built [a comprehensive spike](https://godbolt.org/z/fv9Medo95) of the aggregate-initialization approach and also the proposed "pre-created primitives". There, I added a notion of an `OptionsReader` that somewhat alleviates the mentioned short-coming of...

> We'll inevitably find we need to eg remove a field or change its type, and then be sad. Yep, I agree. The aggregate approach does lack flexibility because of...

Two more general points up for discussion: 1. We should probably reconsider Falko's suggestion of [Type-based algorithm instantiation](https://github.com/randombit/botan/issues/3275) while introducing this builder concept. Certainly not to implement it all at...

Here's another spike that sketches out most of the suggestions above: * let the builder create the `PK_Signer` via [a final `create()`](https://github.com/randombit/botan/pull/4318#issuecomment-2297990007) * allow [lvalues of the Options](https://github.com/randombit/botan/pull/4318#discussion_r1722861968) * boolean...

@randombit Any thoughts on my suggested improvements? I'm happy to adopt this PR and extend it as sketched in the godbolt link from two weeks ago. We do somewhat depend...

> I'm happy to adopt this PR and extend it as sketched in the godbolt link from two weeks ago. @randombit I started working on it with fair progress. Though,...