get type id from the trait object

[peacess]

pub fn get_data_type_id() TypeId
if add the fn , then we can safety convert trait1 object to trait2 object
trait1 object include data and vtable1
trait2 object include data and vtable2

data + vtable1 + get_data_type_id() + trait2 ==>(safety) trait2 object

[bjorn3]

There are multiple ways to support downcasting trait objects to different trait objects. Each has different advantages and disadvantages. There has been a lot of discussion about this in the past, but no proposal has been accepted yet. By the way internals.rust-lang.org is a more suitable location to discuss changes to the rust language.

[jonas-schievink]

Hi! Additions or changes to the language need to go through our RFC process. Before an RFC is written, the feature can also be discussed in our internals forum to find other people interested in it.

Closing in favor of an RFC.

[jonas-schievink]

Trait object upcasting on the other hand is currently being implemented in #86264