Zig developers are warning against the habit of stripping asserts from production builds. An HN discussion highlighted that Zig’s std.debug.assert is a regular function, not a macro, so its argument always evaluates. The language treats asserts as reachable‑code checks that can trigger a panic in checked modes, making them more than optional debug fluff.

Zig offers four build modes—Debug, ReleaseSafe, ReleaseFast and ReleaseSmall—each toggling how asserts behave. In unchecked modes like ReleaseFast, a failing assert leads to undefined illegal behavior rather than a crash, allowing the compiler to propagate unreachable information for aggressive optimizations. Benchmarks show the compiler can elide entire branches, a trick prized by real‑time games.

Because asserts in Zig are ordinary function calls, placing side‑effecting code inside them remains safe even when compiled in ReleaseFast. Disabling them altogether requires a custom wrapper and sacrifices the safety net they provide. The author argues that removing asserts creates silent misbehavior, a risk far worse than the occasional performance hit of keeping them enabled.

Keeping asserts active also aids fuzz testing, as they encode pre‑ and post‑conditions that surface bugs faster than unit tests alone. For teams that rely on Zig’s compile‑time safety, the practical guidance is simple: never disable std.debug.assert in production; instead profile and optimise without sacrificing these critical correctness checks.