slotmap

slotmap provides generational-index arenas in Rust — a pattern where handles (keys) include a generation counter that detects use-after-free at runtime, preventing ABA problems. It ships three variants optimized for different access patterns.

When to use it

Use slotmap when you need an arena with stable handles and individual element removal — entity-component systems, graph nodes, resource managers. Unlike bumpalo (which only supports bulk deallocation), slotmap lets you insert and remove individual elements while keeping existing handles valid.

Generational indices

The key insight: each slot stores a generation counter. When an element is removed and the slot reused, the generation increments. Old keys with stale generations are detected on access, turning use-after-free into a safe, explicit error.