Bikeshedding `Handle` and other follow-up thoughts

There have been two major sets of responses to my proposal for a Handle trait. The first is that the Handle trait seems useful but doesn’t over all the cases where one would like to be able to ergonomically clone things. The second is that the name doesn’t seem to fit with our Rust conventions for trait names, which emphasize short verbs over nouns. The TL;DR of my response is that (1) I agree, this is why I think we should work to make Clone ergonomic as well as Handle; and (2) I agree with that too, which is why I think we should find another name. At the moment I prefer Share, with Alias coming in second.

Handle doesn’t cover everything

The first concern with the Handle trait is that, while it gives a clear semantic basis for when to implement the trait, it does not cover all the cases where calling clone is annoying. In other words, if we opt to use Handle, and then we make creating new handles very ergonomic, but calling clone remains painful, there will be a temptation to use the Handle when it is not appropriate.

In one of our lang team design meetings, TC raised the point that, for many applications, even an “expensive” clone isn’t really a big deal. For example, when writing CLI tools and things, I regularly clone strings and vectors of strings and hashmaps and whatever else; I could put them in an Rc or Arc but I know it just doens’t matter.

My solution here is simple: let’s make solutions that apply to both Clone and Handle. Given that I think we need a proposal that allows for handles that are both ergonomic and explicit, it’s not hard to say that we should extend that solution to include the option for clone.

The explicit capture clause post already fits this design. I explicitly chose a design that allowed for users to write move(a.b.c.clone()) or move(a.b.c.handle()), and hence works equally well (or equally not well…) with both traits

The name Handle doesn’t fit the Rust conventions

A number of people have pointed out Handle doesn’t fit the Rust naming conventions for traits like this, which aim for short verbs. You can interpret handle as a verb, but it doesn’t mean what we want. Fair enough. I like the name Handle because it gives a noun we can use to talk about, well, handles, but I agree that the trait name doesn’t seem right. There was a lot of bikeshedding on possible options but I think I’ve come back to preferring Jack Huey’s original proposal, Share (with a method share). I think Alias and alias is my second favorite. Both of them are short, relatively common verbs.

I originally felt that Share was a bit too generic and overly associated with sharing across threads – but then I at least always call &T a shared reference¹, and an &T would implement Share, so it all seems to work well. Hat tip to Ariel Ben-Yehuda for pushing me on this particular name.

Coming up next

The flurry of posts in this series have been an attempt to survey all the discussions that have taken place in this area. I’m not yet aiming to write a final proposal – I think what will come out of this is a series of multiple RFCs.

My current feeling is that we should add the Hand^H^H^H^H, uh, Share trait. I also think we should add explicit capture clauses. However, while explicit capture clauses are clearly “low-level enough for a kernel”, I don’t really think they are “usable enough for a GUI” . The next post will explore another idea that I think might bring us closer to that ultimate ergonomic and explicit goal.