Is Manual Memory Management Really Necessary? A Look at Zig and Rust

In recent years, two languages have gained traction in the realm of systems programming: Zig and Rust. Both languages are often mentioned as potential alternatives to C/C++ in low-level development, yet they have surprisingly different design philosophies.

In this post, we'll compare Zig and Rust through the lens of "manual memory management." I should note that while I have plenty of experience with Rust, I'm relatively new to Zig. If you spot any mistakes or misinterpretations on the Zig side, please let me know—I'm still learning!

How Rust Guarantees Memory Safety

Let's start with Rust. Rust uses the concepts of ownership and borrowing, which the compiler enforces at compile time through what's commonly known as the borrow checker. Thanks to this mechanism, Rust can eliminate memory errors like double frees and dangling pointers before the program ever runs.

The Upsides

• High level of safety: Memory bugs such as double frees or dangling pointers are caught at compile time
• Concurrent contexts: Rust significantly reduces risks like data races or memory corruption in multithreaded scenarios
• Great for large-scale development: Because the compiler ensures memory correctness across the entire codebase, even big projects benefit from a reduced risk of subtle memory issues

The Downsides

• Learning curve: Concepts like ownership and lifetimes can be tricky at first
• Not everything is "managed automatically": Sometimes, you really do need fine-grained control. Rust has a mechanism for that, but it comes with its own complexity

Rust's unsafe Blocks

For use cases where Rust's safe abstractions aren't quite enough, there's unsafe. This special block lets you perform low-level operations that bypass the borrow checker's usual rules. Common examples include:

• Directly accessing physical addresses in OS kernels or drivers
• Interfacing with C/C++ libraries, manipulating raw pointers
• Controlling data structure layouts and alignment precisely

Of course, "unsafe" comes with a warning: if you misuse pointers or free something twice, the compiler won't stop you anymore. That's why Rust encourages limiting your unsafe blocks to the smallest possible areas—usually just where you do hardware or specialized memory operations. This way, the rest of your code can remain safe and take advantage of Rust's protections.

Zig's Philosophy: "Do Everything by Hand"—But with Optional Safety Checks

Now, on to Zig. Please remember I'm still new to Zig, so if there's a point that needs correction, I'd really appreciate any feedback!

Unlike Rust, Zig doesn't have an ownership system or garbage collection. Instead, you manage allocations and deallocations manually, reminiscent of C. For example, to dynamically allocate an array in Zig, you explicitly call the allocator and then free the memory yourself:

const std = @import("std");

pub fn main() !void {
    var allocator = std.heap.page_allocator;
    const array = try allocator.alloc(u8, 100);
    // Use the array here
    allocator.free(array);
}

That's conceptually similar to malloc/free in C. If you mess up and cause a memory overrun, Zig won't automatically protect you. However, Zig does include safety modes—both at compile time and runtime. In runtime safety mode, the language will perform checks (such as array bounds checking) and trigger a panic if something goes out of range. These safety behaviors depend on default settings and build options, so it's not correct to say "Zig has absolutely zero checks." Instead, it's more accurate to say that Zig is flexible, giving you the option to disable or enable these checks depending on your performance and safety requirements.

The Upsides

• No runtime or GC (by default): This can make binaries smaller and potentially more predictable
• Powerful compile-time execution (CTFE): Metaprogramming in Zig can be done at compile time in a relatively straightforward manner
• Easy cross-compilation: The Zig compiler itself supports many platforms, making cross-compilation simpler
• Optional safety checks: Zig can detect out-of-bounds array access in runtime safety mode, helping catch certain errors

The Downsides

• Manual memory management: If you disable safety checks, memory errors will be your responsibility alone
• No built-in ownership or lifetime checks: The risk of memory bugs can be higher, especially in large codebases that aren't leveraging Zig's optional safety features

When Do You Actually Need Manual Memory Management?

1. Real-Time and High-Performance Scenarios

In game engines or embedded systems, for instance, a garbage collector might cause unpredictable pauses (frame drops or missed deadlines). Manually managing memory lets you control exactly when and where allocations or deallocations happen, helping avoid unexpected performance dips.

2. Operating Systems, Kernels, and Drivers

When working at extremely low level (like OS kernels), you can't rely on a language runtime. There's no GC and often no standard library in the early stages. Directly interfacing with physical addresses is common, so manual memory management is a necessity.

3. Memory Layout Optimization

In large simulations or performance-critical applications, laying out data to optimize cache usage can be crucial. Sometimes you need to place data structures in a specific way to avoid false sharing or improve cache locality, and that often entails custom allocators or memory pools.

A Quick Look at False Sharing

While discussing performance, let's highlight false sharing—a subtle pitfall in multithreaded programming. False sharing occurs when different threads update different variables that happen to lie on the same CPU cache line.

For example, consider this Rust code:

struct Counter {
    value1: u64, // accessed by thread 1
    value2: u64, // accessed by thread 2
}

value1 and value2 look independent, but if they share the same 64-byte cache line, updating one can invalidate the line for the other, triggering expensive cache coherence operations.

Why Performance Suffers

1. Thread 1 updates value1, invalidating the cache line on other cores
2. Thread 2 tries to access value2, causing a cache line reload
3. This invalidation-reload cycle repeats, degrading performance

Potential Solutions

In Rust, you can address this by adding alignment or padding:

use std::sync::atomic::AtomicU64;

#[repr(align(128))]
struct Counter {
    value1: AtomicU64,
    _pad: [u8; 120], // extra padding
    value2: AtomicU64,
}

You can do something similar in Zig, too:

const std = @import("std");

const Counter = struct {
    value1: std.atomic.Value(u64),
    _pad: [120]u8 = undefined,
    value2: std.atomic.Value(u64),

    pub fn init() Counter {
        return .{
            .value1 = std.atomic.Value(u64).init(0),
            .value2 = std.atomic.Value(u64).init(0),
        };
    }
};

Remember: Only optimize after confirming (through profiling) that false sharing is a real bottleneck. Over-optimizing prematurely can harm code readability without tangible performance gains.

Rust's unsafe vs. Zig: Which Is Better?

Some say Rust's unsafe blocks are comparable to Zig's "always-manual" approach, and in a sense, that's correct. In an unsafe block, you can do everything C or Zig can do with pointers. However, there's a key difference:

• Rust: You're mostly protected by the compiler's borrowing and lifetime rules. You only step outside that safety net in unsafe blocks, ideally isolating low-level code to specific places
• Zig: The entire language philosophy centers around manual control, but with optional safety checks you can turn on or off. While it's simpler at heart, mistakes can be punishing if you don't use those checks properly

Conclusion: Pick What Suits Your Project

• Zig is an excellent choice if you want maximum low-level control, minimal runtime overhead, and a straightforward cross-compilation experience. It's also appealing if you prefer a C-like style and don't mind being fully responsible for memory safety—though safety modes can help catch some errors if you choose to enable them
• Personal note: Even though I'm new to Zig, I love how clean and simple its core design is
• Rust is fantastic for team projects, larger codebases, or situations where the compiler's ownership system can significantly reduce bugs. When you do need manual control for performance or hardware-level tasks, you can isolate those parts in unsafe blocks. It strikes a balance between performance and safety that many find invaluable

Ultimately, there's no one-size-fits-all. Think about your performance requirements, development environment, and team preferences, then choose the language that best meets those needs. If you're working in a domain that demands tight memory control with minimal runtime footprint, Zig might be your best bet. If safety and productivity are paramount, Rust is an excellent choice.

References & Further Reading

• The Zig Programming Language
• Rust Book
• Zig vs. Rust discussions on official forums and community resources

I hope you found this post helpful! If you have any comments, corrections (especially regarding Zig, since I'm still learning), or personal experiences to share, please leave a comment. Your input is always appreciated!