Announce major Generator -> Coroutine rename

Author: oli-obk

posts/inside-rust/2023-10-24-coroutines.md

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+---
+layout: post
+title: Generators are dead, long live coroutines, generators are back
+author: oli-obk
+---
+
+We have renamed the unstable `Generator` trait to `Coroutine` and adjusted all terminology accordingly.
+If you want to see all 3800 modified lines of code, you can find the PR [here](https://github.com/rust-lang/rust/pull/116958).
+
+Our `Generator` trait was effectively a coroutine already, so this change was long overdue.
+All nightly users using the `Generator` trait must now update their code to refer to the new feature gate and trait names.
+
+## What is the difference?
+
+A generator is just a convenient way to write `Iterator` implementations.
+This means it's a coroutine that has no arguments and no return type.
+Instead when it returns, that means iteration is over, and the `Iterator::next` method returns `None`.
+
+## Coming full circle
+
+This change is directly motivated for *reintroducing* generators, this time with simpler (`async`/`await` style)
+syntax for creating `Iterator`s. Some discussion about this can be found in the [`gen fn` rfc](https://github.com/rust-lang/rfcs/pull/3513).
+
+Of course such a massive change would be incomplete without the PR to immediately reintroduce a new concept with the name that was just removed,
+so [here](https://github.com/rust-lang/rust/pull/116447) you can see the MVP for `gen` blocks that has very weird diagnostics and may panic on you if you poke it too much.