A type system in programming languages is a way to express and enforce compile time constraints (conventionally, anyway).
zig's type system is pretty straightforward, but its comptime is very powerful and, among other things, can enforce arbitrary compile time constraints. It's not the same as rust's types, but I wonder if it isn't better in many ways.
It's not comparable, comptime is more of an alternative to macros. You can build complex systems with it, but they don't natively give you the algebraic reasoning abilities that the typechecker does, at best you'd have to reimplement it yourself in an ad hoc way. Rust's proc macros are also fully programmable and have comparable expressive power to comptime.
I used Zig in the past (after my "why don't we just write everything simply in C" phase). I don't think I used comptime too much, but I understood why it would be useful.
Now I write Rust and absolutely love it, except for the damn macro edge cases, like not being able to use a known-at-compile-time string for format!() unless it's a literal (I even tried to fake it with more macros, no dice). I think Zig's Andrew Kelley mentioned this exact scenario, if I recall correctly.
It's funny because I do write a lot of code that generates code, but I avoid macros if I can.
Don’t underestimate Zig’s comptime or modern C++’s constexpr. You can use these to prove things about the program at compile-time far beyond the type system. In recent versions of C++, the scope of code that is compile-time verifiable is quite large, nothing like when it was first introduced 15 years ago.
This has limited (but not zero) applicability to memory safety but it has a lot of applicability to many other classes of defect against which Rust offers no special protection. Features like this are why modern C++ is still the language of choice for new software in high-assurance environments at DoD when performance matters. (When performance doesn’t matter it seems to be Java and C#.) These systems often have little or no legacy C++ code as a dependency, so that isn’t a factor.
I have less experience with Zig but this is an area where Rust can’t replicate the safety features of modern C++. With the introduction of compile-time reflection in C++26, this gap will increase. People who aren’t deep in it seriously underestimate what can be verified at compile-time in recent versions of C++ without the use of ugly arcana (which used to be required).
C++ constexpr is a nasty trap. Because after all it says right on the tin that we're getting a constant expression right? So it's as powerful as Rust's const right?
Nope - of course the usual suspects insisted they needed a way to write non-constant expressions and have that somehow "work" anyway. So whereas a const function in Rust genuinely is constant, a constexpr function in C++ might not be, and we only find out whether it was if we force the compiler to do the operation at compile time. If we leave any gap where it can just delay until runtime that's what happens.
You can literally write a random number generator, label it "constexpr" and a modern C++ compiler goes OK, that's not actually constant, but you didn't technically promise it was constant you just used this useless "constexpr" keyword to gesture performatively at the idea of compile time evaluation without promising anything so we'll only complain if you try to use it in a context where I must know the concrete value at compile time.
