The Standard Library as Architecture

Helix’s standard-library types expose its ownership model.

• Vec<Box<dyn Component>> is an ordered, heterogeneous UI layer stack.
• HashMap<ViewId, Selection> lets one document own per-view cursor state.
• Option<T> marks modes and resources that genuinely may not exist.
• Box<dyn FnOnce(...) + Send> is a one-use command carrying captured owned data.
• Arc<ArcSwap<Config>> gives readers cheap configuration snapshots while a reload replaces the shared value.
• std::mem::take temporarily moves accumulated changes or futures out of a borrowed owner so they can be processed safely.
• process handles, atomics, and Duration make external lifecycle and deadlines explicit.

The crucial distinction is between value snapshots and mutation rights. A rope clone is cheap structural sharing suitable for an async operation. An &mut Editor is deliberately scarce and never held across a detached task.

This is a recurring Rust design pattern: clone stable input, move it into work, then return a small result or command to the unique owner.