@lixou I think what you want is a [derive macro](https://doc.rust-lang.org/reference/procedural-macros.html#derive-macros), which is a form of procedural macro.

There is a [proc macro workshop](https://github.com/dtolnay/proc-macro-workshop#attribute-macro-sorted) that will teach you a lot about writing proc macros. The author of the repo had also implemented some of the workshop items, such as [seq](https://github.com/dtolnay/seq-macro), which you can use as reference.

@lixou : https://users.rust-lang.org/t/what-are-blanket-implementations/49904

There are a lot of examples of blanket implementation I think. Here is one example I found just looking around: https://docs.rs/quote/1.0.32/quote/trait.ToTokens.html#impl-ToTokens-for-%26'a+mut+T

So maybe your trait could be implemented via a blanket implementation like this: impl CustomTrait for T where T: Fn...

Although, I still think there is a way to do this via derive macro. An example would be #[tokio::main]. I am not familiar with derive macro to know off of the top of my head how that would be done.