Why Rewriting Everything in Rust Won't Solve All Your Problems

Rust is the tech world's equivalent of the new kid on the block who’s great at sports, gets top grades, and can even play the guitar. It’s safe, fast, and promises to rid your codebase of the infamous memory bugs that have haunted your nightmares. But does that mean you should rewrite all your projects in Rust? Not quite. ?

Rewriting in Rust can be great for certain scenarios, but it’s not a universal remedy for all your software development woes. Let’s dive into why, with some code snippets, analogies, and hopefully a few laughs along the way. ?

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Rust’s Strengths: Why the Hype?

Before we critique Rust, let’s give it its due praise: ?

1. Memory Safety: Rust’s borrow checker eliminates entire classes of bugs like null pointer dereferencing and data races. Amazing! ✅

2. Performance: Rust runs almost as fast as C or C but with far fewer crashes. If you’re building high-performance systems, Rust is your friend. ?

3. Modern Tooling: With Cargo, Rust’s package manager and build tool, dependency management is a breeze compared to some other languages (looking at you, JavaScript). ?

Rust’s mantra is safety, speed, and stability. Who wouldn’t want that? Now, let’s explore why that doesn’t mean you should grab a sledgehammer and demolish your current codebase. ?️

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1. The "Rewrite Fallacy"

Imagine you own a slightly leaky boat. Instead of patching it up, you decide to build an entirely new one from scratch. Sure, the new boat might be sturdier, but the process will take months, cost a fortune, and there’s a chance it won’t float at all. ⛵

Rewriting code is similar. Joel Spolsky’s classic blog post "Things You Should Never Do" warns against throwing away working code. Why? Because rewriting introduces bugs, throws away years of debugging knowledge, and slows progress. Rewriting in Rust amplifies these risks because Rust’s learning curve is steep.

Example: Refactoring vs. Rewriting

Let’s say you have this Python function:

# Python: Calculate factorial

def factorial(n):
    if n == 0:
        return 1
    return n * factorial(n - 1)

Simple, right? But you want the speed and safety of Rust. Here’s what it might look like:

// Rust: Calculate factorial

fn factorial(n: u64) -> u64 {
    match n {
        0 => 1,
        _ => n * factorial(n - 1),
    }
}

Cool, but was the rewrite worth it? For a tiny snippet like this, probably not. The Python code works fine and is easier for new developers to read and maintain. If performance becomes an issue, you could have optimized just this specific function with a Rust library using tools like PyO3, instead of rewriting everything.

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2. Learning Curve: Not Everyone Speaks Rustacean

Rust’s syntax can feel alien to developers used to more traditional languages. Concepts like borrowing, lifetimes, and ownership are powerful but also intimidating. If your team isn’t already familiar with Rust, expect delays and confusion.

A Tale of Borrowing Woes

Consider this simple task: modifying a vector in Rust.

# Python: Calculate factorial

def factorial(n):
    if n == 0:
        return 1
    return n * factorial(n - 1)

Looks fine, but if you forget to use &mut or dereference with *, the borrow checker will scold you. Developers coming from, say, JavaScript or Python might feel like they’re being hazed.

Meanwhile, here’s the equivalent in Python:

// Rust: Calculate factorial

fn factorial(n: u64) -> u64 {
    match n {
        0 => 1,
        _ => n * factorial(n - 1),
    }
}

Much simpler, right? Rust makes you work harder upfront to guarantee safety, which is fantastic for systems programming but overkill for smaller, less error-prone projects.

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3. Not All Code Needs Rust’s Features

Rewriting your personal to-do list app in Rust because "Rust is cool" is like building a birdhouse with industrial-grade steel beams. Over-engineering doesn’t help anyone.

When Rust is Overkill

Let’s say you’re writing a script to rename some files:

Python:

fn main() {
    let mut numbers = vec![1, 2, 3];

    for num in &mut numbers {
        *num += 1;
    }

    println!("{:?}", numbers);
}

Rust:

numbers = [1, 2, 3]

for i in range(len(numbers)):
    numbers[i] += 1

print(numbers)

Rust’s solution is more robust, but if your script will only run once, is the extra complexity worth it? For quick, one-off tasks, high-level scripting languages like Python are often a better choice. ?

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4. Developer Productivity: The Trade-Off

Rust makes you write more code to achieve the same result as other languages. This trade-off is worth it for safety-critical systems but slows you down in environments where speed of development matters more than runtime performance.

Startup Speed vs. Scalability

If you’re building an MVP or prototyping, use a language that lets you iterate quickly. Once you’ve validated your idea and need to scale, you can consider rewriting performance-critical parts in Rust. ?

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5. The "Perfect Tool" Fallacy

No language is perfect. Rust shines for:

• Systems programming (e.g., operating systems, game engines).
• Performance-critical applications.
• Multi-threaded programs where safety matters.

But it’s less ideal for:

• Rapid prototyping.
• Scripting and automation.
• Teams with limited Rust experience.

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Conclusion: Use Rust, But Use It Wisely

Rust is a phenomenal language with groundbreaking features. It deserves the hype, but it also requires significant time and effort to adopt. Rewriting your projects in Rust may not be the miracle solution you’re looking for.

Instead, consider Rust where it makes sense: critical performance bottlenecks, memory-safe APIs, or long-term projects where stability is paramount. For everything else, stick to what works. Remember, the best tool is the one that gets the job done—even if it’s a leaky boat patched with duct tape.

So, don’t toss your Python, JavaScript, or Go codebase into the trash just yet. Rust might be the hero you need—but not for every battle.

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