The `Overwrite` trait and `Pin` · baby steps

In July, boats presented a compelling vision in their post pinned places. With the Overwrite trait that I introduced in my previous post, however, I think we can get somewhere even more compelling, albeit at the cost of a tricky transition. As I will argue in this post, the Overwrite trait effectively becomes a better version of the existing Unpin trait, one that effects not only pinned references but also regular &mut references. Through this it’s able to make Pin fit much more seamlessly with the rest of Rust.

Before I dive into the details, let’s start by reviewing a few examples to show you what we are aiming at (you can also skip to the TL;DR, in the FAQ).

The first change is “mildly” backwards incompatible. I’m not going to worry about that in this post, but I’ll cover the ways I think we can make the transition in a follow up post.

We would really like to add a generator syntax that lets you write an iterator more conveniently.1 For example, given some slice strings: &[String], we should be able to define a generator that iterates over the string lengths like so:

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