In-place initialization

Summary

Evaluate the different approaches to in-place initialization and, together with the lang team, align on a recommended approach.

Motivation

The status quo

There are multiple projects that are running into various problems that can only be solved using a mechanism for in-place initialization. Each project has implemented their own independent and slightly different solution in external crates relying on complex macros at the cost of ergonomics.

It’s time to learn from the extensive amount of experimentation in the ecosystem and create a language feature that provides a shared solution that can be more ergonomic than what is possible in an external crate.

What we propose to do about it

A lot of the work that has happened over the last goal period has been various forms of discussion: >60 zulip threads in the #t-lang/in-place-init channel, many discussions over video call, and long conversations in-person at conferences. There are a few different “classes” of approaches that have come up in these discussions. I want to see each “class” of solution written up in a doc, perhaps using the RFC format, so that we can compare them without having to read through long conversation threads.

For this purpose, we have created a section on the beyond-refs wiki that can hold proposals in one place. We are also planning a workshop at the All-Hands.

At the end of the goal period, we would like to pick and recommend one of the approaches to in-place initialization. Under the stages of development framework, one could say that we want to move from the “we are exploring” phase to the “we have a plan” phase.

Work items over the next year

Sketch out the specific things you are trying to achieve in this goal period. This should be short and high-level – we don’t want to see the design!

Team asks

To recommend a single approach to in-place initialization, we will need the lang team’s input and buy-in on the selected approach.