Function that can return any struct that implements a Trait

[asp2insp]

You can use enums inside of enums, but you cannot restrict the value to one variant of the enum (ie use the enum variant as a top-level type).

Example: Rust Playground

[marcianx]

@JuanPotato

I sort of see where you are going with this, but I still feel like there should be an easier way to do this. I know an implementation of the telegram api in Golang was possible because you could return an object and then switch case for its type. There is a C implementation (not working anymore though) that I might be able to learn something from.

@withoutboats

The reason we can't do what Go does is that types don't carry any runtime type information, so we have basically no reflection capabilities. There's some stuff you can do with the Any trait, maybe that will work for you.

I'd like to emphasize that rust does have sufficient runtime type information for Go-like switching on types via the builtin Any trait, though there are caveats: it's not applicable to types that are constrained by a non-static lifetime since lifetime is strictly a compile-time construct and cannot safely be reconstructed at run-time. So, as long as your types (automatically) implement Any, you can define a trait on which you can iteratively try to cast to different concrete types. The ergonomics for doing that isn't built into the language, and you need any of the many downcasting crates. I authored downcast-rs, which uses only safe code and supports type-parametrized traits.

That being said, you probably want an enum for your case.