Prepare announcement for release 0.9.1

Author: sgued

content/2025-08-20-heapless-091.md

@@ -6,20 +6,18 @@ in_search_index = true
 template = "page.html"
 +++
 
-# Heapless `0.9.1` released
-
-Almost 2 years after the last release, the [heapless](https://github.com/rust-embedded/heapless). The first attempt at a `0.9.0` release was yanked, due to including more breaking changes than intended.  This has been fixed, and `0.9.1`  has been released today.
+Almost 2 years after the last release, the [heapless](https://github.com/rust-embedded/heapless) crate has a new release. The first attempt at a `0.9.0` release was yanked due to including more breaking changes than intended.  This has been fixed, and `0.9.1`  has been released today.
 
 Compared to `0.8.0`, the `0.9.1` release contains a bunch of small everyday improvements and bugfixes. Most users of the library should be able to adapt with minimal changes. For more information, you can check out [the changelog](https://github.com/rust-embedded/heapless/blob/main/CHANGELOG.md). Here are some of the major changes that can improve your usage of the library.
 
 <!-- more -->
 
 # The `View` types
 
-One of the main constraints when working with `heapless` types is that they all have a `const generic`. In a lot of situations, these can be removed thanks to the `View` types.
+One of the main constraints when working with `heapless` types is that they all have a `const generic`. In a lot of situations, these can now be removed thanks to the `View` types.
 
-A lot of embedded firmware will allocated a couple of buffers and pass them around to save on memory.
-To make it easy to change the size of the buffers, a lot of functions will carry along these `const generics`:
+A lot of embedded firmware will allocate a couple of buffers and pass them around to save on memory.
+To make it easy to change the size of the buffers, functions will carry along these `const generics`:
 
 ```rust
 use heapless::Vec;
@@ -28,13 +26,13 @@ struct App{
 }
 
 impl App {
-     pub fn handle_request<const N: usize, const M: usize>(input: &mut Vec<u8, N>, output: &mut Vec<u8, M>) -> Result<(), Error> {
+     pub fn handle_request<const N: usize, const M: usize>(input: &mut Vec<u8, N>, output: &mut Vec<u8, M>) -> Result<(), Error> {
 	     …
      }
 }
 ```
 
-The new `View` variants of the types will enable you to remove the `const generics` while still keeping the same functionality:
+The new `View` variants of the types enable you to remove the `const generics` while still keeping the same functionality:
 
 ```rust
 use heapless::VecView;
@@ -49,10 +47,13 @@ impl App {
 }
 ```
 
-Callsites of the `handle_request` will essentially be able to stay the same, the function will continue to accept `Vec<u8, N>`. So what's the difference between `VecView` and `Vec`?
-There are almost none, both are aliases of the same underlying type `VecInner`. The only limitation that `VecView` has compared to `Vec` is that `VecView` is `!Sized`. This means that you cannot perform anything that would require the compiler to know the size of the `VecView` at compile-time. In practice, you will always need to manipulate `VecView` through pointer indirection (generally a reference). This means you can't just create a `VecView` out of thin air, the `VecView` is a runtime "View" of an existing `Vec`.
+Call sites of `handle_request` will be able to stay the same. The function will continue to accept `&mut Vec<u8, N>`.
+
+So what's the difference between `VecView` and `Vec`?
 
-So how can we obtain a `VecView` ? It's pretty simple: `Vec` can be *coerced* into a `VecView`. [Coercion](https://doc.rust-lang.org/reference/type-coercions.html) (in this case [`Unsized` coercion](https://doc.rust-lang.org/reference/type-coercions.html#r-coerce.unsize)), is a way the compiler can transform one type into another implicitely. In this case, the compiler is capable of converting pointers to a `Vec` (`&Vec<T>`, `&mut Vec<T>`, `Box<T>` etc...) to pointers to a `VecView`, so you can use a reference to a `Vec` when a reference to a `VecView` is exepected:
+There are almost none, both are aliases of the same underlying type `VecInner`. The only limitation of  `VecView` compared to `Vec` is that `VecView` is `!Sized`. This means that you cannot perform anything that would require the compiler to know the size of the `VecView` at compile-time. You will always need to manipulate `VecView` through pointer indirection (generally a reference). This means you can't just create a `VecView` out of thin air. The `VecView` is always a runtime "View" of an existing `Vec`.
+
+So how can we obtain a `VecView` ? It's pretty simple: `Vec` can be *coerced* into a `VecView`. Coercion (in this case [`Unsized` coercion](https://doc.rust-lang.org/reference/type-coercions.html#r-coerce.unsize)), is a way the compiler can transform one type into another implicitly. In this case, the compiler is capable of converting pointers to a `Vec` (`&Vec<T, N>`, `&mut Vec<T, N>`, `Box<Vec<T, N>>` etc...) to pointers to a `VecView` (`&VecView<T>`, `&mut VecView<T>`, `Box<VecView<T>>` etc...), so you can use a reference to a `Vec` when a reference to a `VecView` is expected:
 
 ```rust
 use heapless::{VecView, Vec};
@@ -66,43 +67,65 @@ impl App {
      }
 }
 
-let mut request: Vec<u8; 256> = Vec::new();
-let mut reply: Vec<u8; 256> = Vec::new();
+let mut request: Vec<u8, 256> = Vec::new();
+let mut reply: Vec<u8, 256> = Vec::new();
 
 app.handle_request(&mut request, &mut reply).unwrap();
 ```
 
-If you prefer things to be explicit, the `View` variants of types (`Vec` is not the only datastructure having `View` variants) can be obtained through `vec.as_view()` or through `vec.as_mut_view()`.
+If you prefer things to be explicit, the `View` variants of types (`Vec` is not the only data structure having `View` variants) can be obtained through `vec.as_view()` or through `vec.as_mut_view()`.
 
 The pointer to the `VecView` is the size of 2 `usize`: one for the address of the underlying `Vec`, and one for the capacity of the underlying `Vec`. This is exactly like slices. `VecView<T>` is to `Vec<T, N>` what a slice `[T]` is to an array `[T; N]`.
 Unless you need to store data on the stack, most often you will pass around `&mut [T]` rather than `&mut [T; N]`, because it's simpler. The same applies to `VecView`. Wherever you use `&mut Vec<T, N>`, you can instead use `&mut VecView<T>`.
 
-The `View` types are not available just for `Vec`. There are `View` versions of a lot of heapless types.
+The `View` types are not available just for `Vec`. There are `View` versions of a lot of heapless types:
+- `Vec` has `VecView`
+- `String` has `StringView`
+- `Deque` has `DequeView`
+- `LinearMap` has `LinearMapView`
+- `HistoryBuf` has `HistoryBufView`
+- `BinaryHeap` has `BinaryHeapView`
+- `mpmc::Queue` has `mpmc::QueueView`
+- `spsc::Queue` has `spsc::QueueView`
+  (and now, the producer and consumer structs don't carry the const-generic)
+- `SortedLinkedList` has `SortedLinkedListView`
+
+`IndexMap` and `IndexSet` are the two remaining structures that don't have a `View` type available.
+We hope to be able to use it in the future.
 
 ## Benefits of the view types
 
 The benefits are multiple:
 
 ### Better compatibility with `dyn Traits`
 
-If a trait has a function that takes a generic, it is not `dyn` compatible. By removing the const generic, the `View` types can make `dyn Trait` can pass around data structures without having to hard-code a single size of buffer in the trait definition.
-
-### Better ergonomics
-
-The View types can remove a ton of excess noise from the generics.
+If a trait has a function that takes a generic, it is not `dyn` compatible. By removing the const generic, the `View` types can make `dyn Trait` pass around data structures without having to hard-code a single size of buffer in the trait definition.
 
 ### Better binary size and compile times
 
 When you use const-generics, the compiler needs to compile a new version of the function for each value of the const-generic.
-Removing the const generic means cutting down on duplicated function that are all almost the same, which improves both compile time and the size of the resulting binary.
+Removing the const generic means cutting down on duplicated functions that are all almost the same, which improves both compile time and the size of the resulting binary.
+
+### Better ergonomics
+
+The View types can remove a ton of excess noise from the generics.
 
 # The `LenType` optimization
 
 Most often, buffers in embedded applications will not contain a huge number of items.
-However, until `0.9.1` their capacity was almost always stored as a `usize`, which can often encode much more values than necessary.
+Until `0.9.1` the capacity of the `heapless` data structures were almost always stored as a `usize`, which can often encode much more values than necessary.
+
+In 0.9.1, data structures now have a new optional generic parameter called `LenT`. This type accepts `u8`, `u16`, `u32`, and `usize`, and defaults to `usize` to keep typical uses of the library, simple.
+
+If you are seriously constrained by memory, a `Vec<T, 28>` (equivalent to `Vec<T, 28, usize>`) can become a `Vec<T, 28, u8>`, saving up to 7 bytes per `Vec`. This is not much, but in very small microcontrollers, it can make the difference between a program that uses all the memory available and one that just fits.
+
+# Contributors
 
-In 0.9.1, most data structures now have a new optional generic parameter called `LenT`. This type accepts `u8`, `u16`, `u32`, and `usize`, and defaults to `usize` to keep uses of the library simple.
+This release was made possible by [@Zeenix] joining the embedded working group as part of the libs team to help maintain `heapless` and convincing [@sgued] to do the same.
 
-If you are seriously constrained by memory, a `Vec<T, 28>` can become a `Vec<T, 28, u8>`, saving up to 7 bytes per `Vec`. This is not much, but in very small microcontrollers it can make the difference between a program that uses all the memory available and one that just fits.
+The `View` types were a contributions from [@sgued], and the `LenType` were contributed by [@GnomedDev].
+In total 38 contributors participated in all the other improvements to the crate and helped with maintainance.
 
-This release was made possible by [@sgued] and [@zeenix] joining the embedded working group as part of the libs team.
+[@zeenix]: https://github.com/zeenix
+[@sgued]: https://github.com/sgued
+[@GnomedDev]: https://github.com/GnomedDev