We need (at least) ergonomic, explicit handles

Summary

Continuing my discussion on Ergonomic RC, I want to focus on the core question: should users have to explicitly invoke handle/clone, or not? This whole “Ergonomic RC” work was originally proposed by Dioxus and their answer is simple: definitely not. For the kind of high-level GUI applications they are building, having to call cx.handle() to clone a ref-counted value is pure noise. For that matter, for a lot of Rust apps, even cloning a string or a vector is no big deal. On the other hand, for a lot of applications, the answer is definitely yes – knowing where handles are created can impact performance, memory usage, and even correctness (don’t worry, I’ll give examples later in the post). So how do we reconcile this?This blog argues that we should make it ergonomic to be explicit. This wasn’t always my position, but after an impactful conversation with Josh Triplett, I’ve come around. I think it aligns with what I once called the soul of Rust: we want to be ergonomic, yes, but we want to be ergonomic while giving control.I like Tyler Mandry’s Clarity of purpose contruction, “Great code brings only the important characteristics of your application to your attention”. The key point is that there is great code in which cloning and handles are important characteristics, so we need to make that code possible to express nicely. This is particularly true since Rust is one of the very few languages that really targets that kind of low-level, foundational code.This does not mean we cannot (later) support automatic clones and handles. It’s inarguable that this would benefit clarity of purpose for a lot of Rust code. But I think we should focus first on the harder case, the case where explicitness is needed, and get that as nice as we can; then we can circle back and decide whether to also support something automatic. One of the questions for me, in fact, is whether we can get “fully explicit” to be nice enough that we don’t really need the automatic version. There are benefit...