GoKawiilZig Adds Pointer Stability Locks to std.ArrayList
Zig's main branch now supports pointer stability locks for std.ArrayList, a memory-safety mechanism previously introduced for Hash Map containers in 2024. Developers can call lockPointers() when holding pointers or slices into an ArrayList, then unlockPointers() once those references are no longer needed, preventing use-after-free bugs caused by reallocation. The feature originated from a pull request opened by contributor Leo Emar-Kar in 2025 and was documented by Robbie Lyman.
GoKawiil's interpretation of the reporting above, not reported fact.
ArrayLists can silently move their backing memory when they grow, invalidating any pointers or slices taken earlier—a classic source of segfaults in systems languages. By extending the lock mechanism from Hash Maps to ArrayLists, Zig gives developers a built-in way to catch these bugs at compile or runtime rather than discovering them through crashes in production. This reflects Zig's ongoing effort to improve memory safety without sacrificing manual control over allocation.
- Zig's std.ArrayList now supports lockPointers()/unlockPointers() for pointer stability.
- The feature extends a safety technique first used in std Hash Map containers in 2024.
- It targets a common bug class where slices into a growing ArrayList become invalid after reallocation.
Source: ziglang.org, 2026-08-30
Published there as: “Zig: Pointer Stability for ArrayLists”
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