Merge pull request #1404 from TBoshoven/patch-1

Typo in 2024-09-05-impl-trait-capture-rules.md

Author: ehuss

posts/2024-09-05-impl-trait-capture-rules.md

@@ -102,9 +102,9 @@ fn process<'c, T> {
 }
 ```
 
-Here the `process` function applies `context.process` to each of the elements in `data` (of type `T`). Because the return value uses `context`, it is declared as `+ 'c`. Our real goal here is to allow the return type to use `'c`; writing `+ 'c` achieves that goal because `'c` not appears in the bound listing. However, while writing `+ 'c` is a convenient way to make `'c` appear in the bounds, also means that the hidden type must outlive `'c`. This requirement is not needed and will in fact lead to a compilation error in this example ([try it on the playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=b742fbf9b083a6e837db0b170489f34a)).
+Here the `process` function applies `context.process` to each of the elements in `data` (of type `T`). Because the return value uses `context`, it is declared as `+ 'c`. Our real goal here is to allow the return type to use `'c`; writing `+ 'c` achieves that goal because `'c` now appears in the bound listing. However, while writing `+ 'c` is a convenient way to make `'c` appear in the bounds, also means that the hidden type must outlive `'c`. This requirement is not needed and will in fact lead to a compilation error in this example ([try it on the playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=b742fbf9b083a6e837db0b170489f34a)).
 
-The reason that this error occurs is a bit subtle. The hidden type is an iterator type based on the result of `data.into_iter()`, which will include the type `T`. Because of the `+ 'c` bound, the hidden type must outlive `'c`, which in turn means that `T` must outlive `'c`. But `T` is a generic parameter, so the compiler requires a where-clause like `where T: 'c`. This where-clause means "it is safe to create a reference with lifetime `'c` to the type `T`". But in fact we don't create any such reference, so the where-clause should not be needed. It is only needed because used the convenient-but-sometimes-incorrect workaround of adding `+ 'c` to the bounds of our `impl Trait`.
+The reason that this error occurs is a bit subtle. The hidden type is an iterator type based on the result of `data.into_iter()`, which will include the type `T`. Because of the `+ 'c` bound, the hidden type must outlive `'c`, which in turn means that `T` must outlive `'c`. But `T` is a generic parameter, so the compiler requires a where-clause like `where T: 'c`. This where-clause means "it is safe to create a reference with lifetime `'c` to the type `T`". But in fact we don't create any such reference, so the where-clause should not be needed. It is only needed because we used the convenient-but-sometimes-incorrect workaround of adding `+ 'c` to the bounds of our `impl Trait`.
 
 Just as before, this error is obscure, touching on the more complex aspects of Rust's type system. Unlike before, there is no easy fix! This problem in fact occurred frequently in the compiler, leading to an [obscure workaround called the `Captures` trait](https://github.com/rust-lang/rust/issues/34511#issuecomment-373423999). Gross!