[codeflo]

I don't think that would work in general: trait methods can have signatures for which you can't synthesize an implementation for the sum type (something that takes a second Self as an argument, like std::ops::Add, comes to mind).

For object-safe traits where this would be possible, you can at least do this at the cost of an allocation, as you probably know:

  fn some_func() -> Box<dyn SomeTrait> {
      if some_condition {
          Box::new(a)
      } else {
          Box::new(b)
      }
  }