How can dynamically sized Vec<T> be using on STM32?

[johnthagen]

Cross post from rust-lang/rfcs#2480 (comment)

When evaluating using Rust for an embedded project at work, not having dynamic containers was a big drawback at the time compared with C++11/14 where the gcc-arm-embedded toolchain had versions of std::string and std::vector<T>. (C++ has it's own set of drawbacks, like exception-based error handling APIs, but in this one, fundamental case, it had a leg up).

Is there a way (even it's nightly) to use Vec<T> on something like the STM32F3DISCOVERY? It was a hard sell to recommend Rust over C++ without being able to safely use the heap.

Edit: We used heapless in some tutorials but we wanted to have true heap access available like is available for C++11/14 and the gcc-arm-embedded toolchain.

[therealprof]

https://crates.io/crates/heapless

[johnthagen]

@therealprof Thanks, yeah I had seen heapless and I changed the title to be more clear that we'd like to actually use the heap for true dynamically sized containers. heapless requires a fixed size up front.

[therealprof]

You can use alloc-cortex-m to create a heap and combine it with heapless.

[japaric]

@johnthagen what @therealprof said. The quickstart template has an example: https://github.com/rust-embedded/cortex-m-quickstart/blob/master/examples/allocator.rs

[japaric]

(you don't need to specifically use alloc-cortex-m; any global_allocator will do)

[johnthagen]

@japaric Is this mentioned in the Discovery Book? And if not, would you accept a PR to add it? I think this would be a really great addition!

[johnthagen]

(For anyone else finding this issue in the future, the embedded book has some discussion on this as well.)

[therealprof]

I think this would be more appropriate for the book and/or the embeddonomicon with a reference in the discovery book. Any contributions in that directions would certainly be welcome.

[jamesmunns]

I think we should also note (last time I checked) that alloc-cortex-m requires nightly rust to operate.

[johnthagen]

I think we should also note (last time I checked) that alloc-cortex-m requires nightly rust to operate.

Correct, this RFC is currently being discussed to potentially stabilize alloc: rust-lang/rfcs#2480

[johnthagen]

alloc is on track to stabilize for Rust 1.36.0: rust-lang/rust#59675