let bar: Result<T, E> = ...;
let foo = bar.inspect(|value| log::debug("{}", value));

is equivalent to

let bar: Result<T, E> = ...;
let foo = bar.map(|value| {
    log::debug("{}", value);
    value
});

Looks vaguely like Stream::peek from Java, I think? There's an equivalent method in Iterator::inspect.

it's just a way to use map with a reference instead of the value, by what I understood.

could be usefull for logging values in a Result so you can see it. However I think you can already do that by just mapping and returning the variable.

Yeah, I thought of runtime duck typing when I saw it, which is essentially what an ECS is.

It would be pretty cool to go the next step and be able to find and call methods or discover trait implementations on the type that may not be in the signature. So something like how Go can conditionally type asset an interface to a different interface. I don't know if that's possible in a zero cost way (probably not), but it would be interesting.

Yeah, Rust can't have proper reflection, since there's no external runtime environment that keeps track of your state. Any such smartness either has to be compiled-in (which is how std::any and macros work) or you can implement something to keep track of this state at runtime, as if you were partially building a runtime environment.

Isn't RTTI for polymorphic classes and stored in (or around) vtables?