Question 1

rpds vs im-rs: which is better for persistent data structures in Rust?

Accepted Answer

rpds offers more data structures like queues and red-black trees, with explicit thread safety via Arc/Rc, while im-rs is known for its performance and simpler API. Choose rpds for embedded (no_std) support or specific structures; im-rs for general-purpose use with a focus on speed.

Question 2

How to serialize rpds data structures with serde?

Accepted Answer

Enable the 'serde' feature in Cargo.toml, then use derive or impl Serialize/Deserialize. For example, add `rpds = { version = "*", features = ["serde"] }` to dependencies, and structures like HashTrieMap will automatically support serialization.

Question 3

Is rpds thread-safe by default?

Accepted Answer

No, thread safety is opt-in. By default, it uses Rc for single-threaded performance. Use new_sync() or _sync macros to create Arc-based versions for multi-threading, but this incurs a performance cost.

Question 4

What's the performance impact of using rpds compared to std::collections?

Accepted Answer

rpds adds overhead due to persistence and reference counting, making operations slower for mutable cases. However, for immutable updates with versioning, it's more memory-efficient. Benchmarks in the README show Arc variants can be twice as slow as Rc.

Question 5

Can I use rpds in an embedded Rust project?

Accepted Answer

Yes, by disabling the default 'std' feature in Cargo.toml (e.g., `rpds = { version = "*", default-features = false }`). This allows use in no_std environments, though some features like serialization require enabling additional features.

Question 6

How do I switch between Rc and Arc in rpds?

Accepted Answer

Use the archery crate's pointer kinds: specify the type parameter like `Vector<u32, archery::ArcK>` for Arc or `archery::RcK` for Rc. Alternatively, use new_sync() for Arc or standard new() for Rc-based structures.

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