Understanding Rust: Memory Safety, Ownership, Borrowing, and Its Impact on Front‑End Development

This article is selected from the Tencent Cloud Developer Community’s original column, authored by Tencent front‑end engineer Yu Long. It provides an analysis of Rust, aiming to share experience and help developers interested in this language.

About Rust

Rust is a strongly typed, compiled, memory‑safe programming language. It started as a personal project by Graydon Hoare in 2009, received sponsorship from Mozilla in 2009, and achieved self‑hosting in 2010 (the compiler was written in Rust).

Mozilla used Rust to build the next‑generation browser engine Servo; the Servo CSS engine was integrated into Firefox in 2017. Rust was originally intended to replace C/C++ for large‑scale low‑level projects such as operating systems and browsers, but its safety guarantees attracted front‑end developers, leading to a growing ecosystem.

Memory Safety – Rust’s Killer Feature

Most mainstream languages fall into two categories: those with automatic garbage collection (e.g., Go, Java, JavaScript) and those requiring manual memory management (C, C++). Stack memory is automatically managed by scope, while heap memory requires explicit allocation and deallocation.

In languages with manual memory management, a heap allocation returns a pointer stored on the stack. The programmer must decide when to free the memory, which can lead to leaks, double frees, or use‑after‑free bugs.

Rust introduces a novel memory‑management model: the compiler, together with the programmer, enforces a set of rules (ownership and borrowing) that allow the compiler to determine at compile time whether a memory block is still in use. Consequently, Rust can insert the necessary deallocation code without a runtime garbage collector.

No GC algorithm or runtime is needed; memory is reclaimed automatically by the compiler‑generated code.

If the code compiles, it is guaranteed to be memory‑safe.

(1) Implementation Principle

Rust’s memory‑safety mechanism is based on the ownership system, which consists of two core concepts: ownership and borrowing.

(2) Ownership

Every value, including pointers, is bound to a variable that owns it. For example:

let
str =
"hello"

When the variable’s scope ends, the value is automatically dropped. For immutable strings stored on the stack, copying the value creates a new independent copy:

let
str =
"hello world"
;
let
str2 = str;
println!("{}", str);
println!("{}", str2);

For heap‑allocated, mutable strings (`String`), the same code results in a compile‑time error because ownership can only belong to one variable at a time:

fn main() {
let
str =
String
::
from
(
"hello world"
);
let
str2 = str; // move occurs here
println!("{}", str);
// error: value borrowed after move
println!("{}", str2);
}

Ownership transfer also happens when passing a value to a function or returning it from a function.

Borrowing

Although a value has a single owner, it can be temporarily borrowed. The following code borrows a mutable `String` so that the function can modify it without taking ownership:

fn main() {
let
mut str1 =
String
::
from
(
"hello world"
);
  add_str(&mut str1,
"!!!"
);
println!("{}", str1);
}
fn add_str(str_1: &mut
String
, str_2: &str) {
str_1.push_str(str_2);
}

Borrowing eliminates the need for complex reference‑counting garbage collectors while preserving safety.

Other Rust Features

No inheritance, only composition (similar to Go).

Powerful package manager `cargo` with isolated dependencies.

Advanced language features: pattern matching, `Option` instead of `null`, native async support, etc.

Impact on Front‑End Development

Rust is becoming a perfect C++ alternative for front‑end tooling and WebAssembly (WASM) modules.

(1) High‑Performance Tools

Tools such as swc (a Rust‑based Babel alternative), Rome (a comprehensive JavaScript toolchain), and RSLint (a Rust‑based ESLint replacement) demonstrate Rust’s ability to deliver performance gains of dozens of times over traditional JavaScript tools.

(2) WASM

Rust’s zero‑runtime design makes it ideal for compiling to WASM, where a large runtime would bloat the bundle. The official compiler and `wasm‑pack` enable straightforward conversion of Rust libraries to WASM modules.

Example of a Rust library prepared for WASM:

#![deny(warnings)]
#![allow(clippy::unused_unit)]
// import crates
use std::sync::Arc;
use anyhow::{Context, Error};
use once_cell::sync::Lazy;
use swc::{config::{ErrorFormat, JsMinifyOptions, Options, ParseOptions, SourceMapsConfig}, try_with_handler, Compiler};
use swc_common::{comments::Comments, FileName, FilePathMapping, SourceMap};
use swc_ecmascript::ast::{EsVersion, Program};
use wasm_bindgen::prelude::*;
#[wasm_bindgen(js_name = "transformSync", typescript_type = "transformSync", skip_typescript)]
pub fn transform_sync(s: &str, opts: JsValue, experimental_plugin_bytes_resolver: JsValue) -> Result<JsValue, JsValue> {
// implementation omitted for brevity
}

After building with:

wasm-pack build --scope swc -t nodejs --features plugin

the generated files (`binding_core_wasm.js`, `binding_core_wasm_bg.wasm`, etc.) can be imported in JavaScript and used directly:

// index.js
const wasm = require('./pkg/binding_core_wasm');
console.log(wasm.transformSync(code, settings));

This workflow shows how a Rust library can be turned into a lightweight, high‑performance WASM module for front‑end consumption.

Challenges When Learning Rust

Rust’s strict rules can be intimidating. For example, variable declarations are immutable by default (`let a = 1;`), and mutability must be explicitly requested (`let mut a = 1;`). Such design choices impose a mental overhead on developers coming from other languages.

Overall, while Rust offers powerful safety guarantees and performance benefits, newcomers should be prepared for a steep learning curve.

Author: Yu Long, Tencent Front‑End Engineer, contributor to the Tencent Cloud Developer Community.