I seriously don’t get it.
fn add(a: i32, b: i32) -> i32 { … }
trait Handler {
fn handle<'a>(&self, input: &'a str) -> Result<&'a str, HandlerError>;
}
fn process_handler<'a>(
handler: Box<dyn Handler + 'a>,
input: &'a str,
) -> Result<&'a str, HandlerError> {
handler.handle(input)
}You choose as your example a pretty advanced use case.
In the places where you need to add lifetime annotations, it's certainly useful to be able to see them in the types, rather than relegate them to the documentation like in C++; cf. all the places where C++'s STL has to mention iterator and reference invalidation.
The handler function isn't actually unnecessary, or at least, it isn't superfluous: by default, the signature would include 'a on self as well, and that's probably not what you actually want.
I do think that the example basically boils down to the lifetime syntax though, and yes, while it's a bit odd at first, every other thing that was tried was worse.
To clarify, I meant the 'a in `Box<dyn Handler + 'a>` in the definition of `process_handler` is unnecessary. I'm not saying that the <'a> parameter in the definition of Handler::handle is unnecessary, which seems to be what you think I said, unless I misunderstood.