This post shows how versatile Zig's comptime is not only in terms of expressing what to pre-compute before the program ever runs, but also for doing arbitrary compile time bug-checks like these. At least to me, the former is a really obvious use-case and I have no problem using that to my advantage like that. But I often seem to overlook the latter, even though it could prove really valuable.
This is one the reasons I find it so silly when people disregard Zig «because it’s just another memory unsafe language»: There’s plenty of innovation within Zig, especially related to comptime and metaprogramming. I really hope other languages are paying attention and steals some of these ideas.
«inline else» is also very powerful tool to easily abstract away code with no runtime cost.
This isn’t intended as flamebait. I’m trying to understand Zig’s long-term positioning and design philosophy. I have serious confusion about the type of problems Zig is aiming to solve. In my view, Zig is not solving the actual hard problems in systems programming and it doesn't have the foundation to either.
Memory safety? Still entirely manual. Race conditions? Nothing in the language prevents them. There’s no ownership model, no lifetime analysis, no way to tie resource management to the type system. Compare that to Rust’s borrow checker or modern C++’s RAII and concepts. Zig’s type system is shallow. comptime is nice for generating code, but it doesn’t give you formal guarantees or expressive power for invariants, safety, or correctness.
The type system itself has no serious formal grounding. It can’t encode complex invariants, can’t track aliasing, can’t enforce concurrency safety and can’t model safe resource lifetimes. These aren’t academic extras — they’re exactly what decades of research in programming languages, operating systems and concurrent computing tell us you need to scale safety and correctness. Zig ignores them. Performance? When the policy is in the type (allocator choice, borrowing/ownership, fusion shape), Rust/C++ compilers can specialize, inline, and eliminate overhead. In Zig, the same policies are usually runtime values or conventions, which means more indirect calls, more defensive copies and fewer whole-program optimizations.
Concurrency is another major gap and in a real systems language, it cannot be an afterthought. Even if Zig isn’t currently aiming to solve concurrency or safety, a “serious” systems language inevitably has to, because these are the problems that determine scalability, maintainability and security over decades. The async model in Zig is little more than manual coroutine lowering: the compiler rewrites your function into a state machine and leaves correctness entirely to the programmer. There’s no structured concurrency, no safe cancellation, no prevention of shared-state hazards. Without a concurrency model that integrates into the type system, you can’t make guarantees about thread safety or race freedom and you end up relying entirely on discipline (which doesn’t scale).
Even in its most-touted features, Zig seems to be solving syntactic sugar problems, not the important systems problems. defer and errdefer? They’re effectively cleaner syntax for patterns C has had for decades through GNU’s __attribute__((cleanup)) or macro-based scope guards. Error unions? A nice alternative to out-parameters but just syntactic polish over an old idea. comptime? A more integrated macro system but still aimed at reducing boilerplate rather than providing deeper correctness guarantees.
The allocator interface? Another missed opportunity. Zig could have made it type-aware, preventing allocator misuse and catching entire classes of errors at compile time. Instead, it’s basically malloc/free with slightly cleaner function signatures. No safety net, no policy enforcement.
Zig discards decades of research in type systems, concurrency models, safety guarantees, and memory management, then reimplements C with a few ergonomic wins and leaves the hard problems untouched. It’s a restart without the research and not systems language evolution.
I am not a Rust fanatic but by contrast if you’re moving away from C++ or C, Rust actually tackles the big issues. It enforces memory safety without a garbage collector, prevents data races in safe code through its ownership and type system, offers structured concurrency with async/await and has been battle-tested in production for everything from browser engines to operating systems to databases. It is built on decades of progress and integrates those lessons into a language designed to scale correctness and performance together.
In my own code (primarily C++ and Rust), Zig wouldn’t solve a single core problem I face. Memory safety would still be my responsibilit...
Is there a reason the Zig compiler can't perform type-narrowing for `u` within the `U::A(_) | U::B(_)` "guard", rendering just the set of 2 cases entirely necessary and sufficient (obviating the need for any of the solutions in the blog post)?
I'm not familiar with Zig, but also ready to find out I'm not as familiar with type systems as I thought.
Just having a comptime unreachable feature seems pretty cool. Common C++ compilers have the worst version of this with __builtin_unreachable() -- they don't do any verification the site is unreachable, and just let the optimizer go to town. (I use/recommend runtime assert/fatal/abort over that behavior most days of the week.)
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[ 3.1 ms ] story [ 36.1 ms ] threadFails to compile in Rust.
«inline else» is also very powerful tool to easily abstract away code with no runtime cost.
Memory safety? Still entirely manual. Race conditions? Nothing in the language prevents them. There’s no ownership model, no lifetime analysis, no way to tie resource management to the type system. Compare that to Rust’s borrow checker or modern C++’s RAII and concepts. Zig’s type system is shallow. comptime is nice for generating code, but it doesn’t give you formal guarantees or expressive power for invariants, safety, or correctness.
The type system itself has no serious formal grounding. It can’t encode complex invariants, can’t track aliasing, can’t enforce concurrency safety and can’t model safe resource lifetimes. These aren’t academic extras — they’re exactly what decades of research in programming languages, operating systems and concurrent computing tell us you need to scale safety and correctness. Zig ignores them. Performance? When the policy is in the type (allocator choice, borrowing/ownership, fusion shape), Rust/C++ compilers can specialize, inline, and eliminate overhead. In Zig, the same policies are usually runtime values or conventions, which means more indirect calls, more defensive copies and fewer whole-program optimizations.
Concurrency is another major gap and in a real systems language, it cannot be an afterthought. Even if Zig isn’t currently aiming to solve concurrency or safety, a “serious” systems language inevitably has to, because these are the problems that determine scalability, maintainability and security over decades. The async model in Zig is little more than manual coroutine lowering: the compiler rewrites your function into a state machine and leaves correctness entirely to the programmer. There’s no structured concurrency, no safe cancellation, no prevention of shared-state hazards. Without a concurrency model that integrates into the type system, you can’t make guarantees about thread safety or race freedom and you end up relying entirely on discipline (which doesn’t scale).
Even in its most-touted features, Zig seems to be solving syntactic sugar problems, not the important systems problems. defer and errdefer? They’re effectively cleaner syntax for patterns C has had for decades through GNU’s __attribute__((cleanup)) or macro-based scope guards. Error unions? A nice alternative to out-parameters but just syntactic polish over an old idea. comptime? A more integrated macro system but still aimed at reducing boilerplate rather than providing deeper correctness guarantees.
The allocator interface? Another missed opportunity. Zig could have made it type-aware, preventing allocator misuse and catching entire classes of errors at compile time. Instead, it’s basically malloc/free with slightly cleaner function signatures. No safety net, no policy enforcement.
Zig discards decades of research in type systems, concurrency models, safety guarantees, and memory management, then reimplements C with a few ergonomic wins and leaves the hard problems untouched. It’s a restart without the research and not systems language evolution.
I am not a Rust fanatic but by contrast if you’re moving away from C++ or C, Rust actually tackles the big issues. It enforces memory safety without a garbage collector, prevents data races in safe code through its ownership and type system, offers structured concurrency with async/await and has been battle-tested in production for everything from browser engines to operating systems to databases. It is built on decades of progress and integrates those lessons into a language designed to scale correctness and performance together.
In my own code (primarily C++ and Rust), Zig wouldn’t solve a single core problem I face. Memory safety would still be my responsibilit...
https://godbolt.org/z/P1r49nTWo
I'm not familiar with Zig, but also ready to find out I'm not as familiar with type systems as I thought.