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Safe Rust turns the use-after-free, double-free, and forgot-to-free bugs that plagued Bun's error paths into compiler errors, thanks to RAII-like automatic cleanup via Drop.

Jarred Sumner explains the technical reason for choosing Rust: its ownership model catches the exact class of memory bugs that had been hurting Bun, at compile time. ✦ AI generated

Jarred Sumner · Simon Willison's Weblog · 2026-07-08 · original ↗

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A large percentage of bugs from that list are use-after-free, double-free, and "forgot to free" in an error path. In safe Rust, these are compiler errors and RAII-like automatic cleanup with Drop.

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✳ Bun ✳ Rust ✳ Zig

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extends → Bun's crashes largely came from mixing garbage-collected memory with manually-managed memory, a combination so uncommon that no language is really designed to handle it safely, which is why he grew tired of Bun's bugfix list and worried about crashes.Jarred Sumner · Simon Willison's Weblog