FAQ

Why does dequeue require Clone in standard mode?

Standard mode stores items in a Vec<T> and copies them out on dequeue. This is a deliberate simplicity trade-off for single-threaded use.

Concurrent modes (SPSC, MPSC) use MaybeUninit<T> to move items instead of cloning, so they only require T: Send.

Can I use a const for capacity?

No. Procedural macros operate on token streams before const evaluation happens. The capacity must be a literal integer.

// This works:
#[ring_buffer(256)]
struct Buffer(i32);

// This does NOT work:
const SIZE: usize = 256;
#[ring_buffer(SIZE)]  // Error: expected literal
struct Buffer(i32);

How does this compare to VecDeque?

Use VecDeque when you need a growable deque with a rich API. Use ring-buffer-macro when you need fixed-size, bounded buffers — especially in concurrent or embedded contexts.

What about MPMC (multi-producer, multi-consumer)?

MPMC was included in an early version but removed in v0.2.0 due to reliability issues. Correct MPMC requires significantly more complex synchronization. For MPMC needs, use established crates like crossbeam-channel or flume.

What Rust edition is required?

Rust 2021 edition (edition = "2021" in Cargo.toml). The crate uses syn 2.0, quote 1.0, and proc-macro2 1.0 as build dependencies.

The macro isn't expanding correctly

Common issues:

• Must be a tuple struct — struct Buffer(i32), not struct Buffer { data: i32 }
• Exactly one field required — Zero or multiple fields will produce a compile error
• Capacity must be a positive integer literal — No constants, expressions, or type parameters
• power_of_two requires 2^n capacity — 256, 512, 1024 are valid; 100, 300 are not

Use cargo expand to see the generated code if you suspect a macro expansion issue:

cargo install cargo-expand
cargo expand

Can I have multiple fields?

No. The macro requires exactly one field — the element type. The tuple struct is transformed into a named struct with internal fields (data, head, tail, size, capacity). Your single field becomes the type parameter for the internal Vec<T>.

How do I contribute?

The project is open source under the MIT license. Contributions are welcome.

• 1.Fork the repository on GitHub
• 2.Create a feature branch
• 3.Run the test suite with cargo test
• 4.Submit a pull request

Repository: github.com/0xsouravm/ring-buffer-macro