Interop Basics

10 examples for choosing how Rust talks to Python, Node.js, C/C++, and other runtimes.

Prerequisites

• Rust 1.97.0 (edition 2024)
• Clear ownership of which language owns the process and the GC heap

Basic Examples

1. Decision Matrix

Pick one primary boundary per integration point.

2. Who Owns main?

Rust owns main     -> embed Python/JS via FFI (PyO3, Neon)
Host owns main     -> export Rust as library (cdylib/staticlib)

The owner controls initialization, signal handling, and allocator choice.

3. Stable ABI Requirement

#[repr(C)]
pub struct Point {
    pub x: f64,
    pub y: f64,
}

• C/C++ interop needs repr(C) and extern "C"
• Rust-to-Rust across crates does not need C ABI
• Never expose String or Vec in C headers

Related: Exposing a Rust Library to C/C++

4. Error Mapping Pattern

#[repr(C)]
pub enum Status {
    Ok = 0,
    InvalidInput = 1,
    Oom = 2,
}

Map Rust Result to integer codes or out-parameters at the boundary.

5. Memory Ownership Contract

Rust allocates -> Rust frees (export mylib_free)
C allocates    -> C frees
Copy at boundary -> safest default for small data

Document who frees every pointer in the header.

Related: Data Marshalling

6. PyO3 Quick Peek

use pyo3::prelude::*;
 
#[pyfunction]
fn add(a: i64, b: i64) -> PyResult<i64> {
    Ok(a + b)
}

Python calls Rust for hot paths. Rust calls Python for orchestration when needed.

Related: PyO3

7. napi-rs Quick Peek

#[napi]
pub fn fib(n: u32) -> u32 {
    match n {
        0 => 0,
        1 => 1,
        _ => fib(n - 1) + fib(n - 2),
    }
}

Generates TypeScript types for Node consumers automatically.

Related: Node.js with napi-rs

8. When WASM Beats Native FFI

• Cross-platform plugins without per-OS builds
• Sandboxed untrusted code
• Same module in browser and edge runtime

Related: Embedding Rust in Other Runtimes

Intermediate Examples

9. maturin for Python Packaging

maturin develop
python -c "import myrust; print(myrust.add(1, 2))"

Builds wheels with Rust inside for pip install.

Related: maturin

10. Integration Checklist

• Ownership rules written in README and header
• Panics caught at FFI boundary
• CI builds all target triples you ship
• Integration tests in the host language
• Semver policy for the public boundary API

Stack versions: This page was written for Rust 1.97.0 (edition 2024), Tokio 1.x, Axum 0.8, serde 1.0, sqlx 0.8, clap 4, and Polars 0.46+.