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Update playground error messages

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Thalia Archibald
2025-08-21 18:18:20 -06:00
parent bae61dd786
commit 1ba06fe61c
8 changed files with 23 additions and 20 deletions
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8
blog/content/edition-2/posts/12-async-await/index.md
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@@ -634,21 +634,21 @@ In addition to changing `Box::new` to `Box::pin`, we also need to add the new `_
When we [try to run our adjusted example](https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=961b0db194bbe851ff4d0ed08d3bd98a) now, we see that it no longer works:
```
error[E0594]: cannot assign to data in a dereference of `std::pin::Pin<std::boxed::Box<SelfReferential>>`
error[E0594]: cannot assign to data in dereference of `Pin<Box<SelfReferential>>`
--> src/main.rs:10:5
|
10 | heap_value.self_ptr = ptr;
| ^^^^^^^^^^^^^^^^^^^^^^^^^ cannot assign
|
= help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::pin::Pin<std::boxed::Box<SelfReferential>>`
= help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `Pin<Box<SelfReferential>>`
error[E0596]: cannot borrow data in a dereference of `std::pin::Pin<std::boxed::Box<SelfReferential>>` as mutable
error[E0596]: cannot borrow data in dereference of `Pin<Box<SelfReferential>>` as mutable
--> src/main.rs:16:36
|
16 | let stack_value = mem::replace(&mut *heap_value, SelfReferential {
| ^^^^^^^^^^^^^^^^ cannot borrow as mutable
|
= help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `std::pin::Pin<std::boxed::Box<SelfReferential>>`
= help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `Pin<Box<SelfReferential>>`
```
Both errors occur because the `Pin<Box<SelfReferential>>` type no longer implements the `DerefMut` trait. This is exactly what we wanted because the `DerefMut` trait would return a `&mut` reference, which we wanted to prevent. This only happens because we both opted-out of `Unpin` and changed `Box::new` to `Box::pin`.