#ffi #code-generation #bindings


The polyglot bindings generator for your library (C#, C, Python, …). 🐙

23 unstable releases (3 breaking)

new 0.4.2 Jul 28, 2021
0.4.1 Jul 27, 2021
0.3.2 Jul 26, 2021
0.2.5 Jul 6, 2021
0.1.16 Jun 27, 2021

#27 in FFI

Download history 85/week @ 2021-06-11 102/week @ 2021-06-18 65/week @ 2021-06-25 93/week @ 2021-07-02 9/week @ 2021-07-09 49/week @ 2021-07-16 65/week @ 2021-07-23

150 downloads per month
Used in 4 crates

MIT license


Latest Version docs MIT Rust Rust

Interoptopus 🐙

The polyglot bindings generator for your library (C#, C, Python, ...)


  • Imagine you are writing this cool API and want everyone to use it.
  • Everyone else, however, is running Unity, C, Python, ...
  • "Not a problem", you say, "I'll just use Interoptopus".

And you'll live happily* ever after.

*Actual results may depend on other life choices.

Code you write ...

use interoptopus::{ffi_function, ffi_type, inventory};

pub struct Vec2 {
    pub x: f32,
    pub y: f32,

pub extern "C" fn my_function(input: Vec2) {
    println!("{}", input.x);

inventory!(ffi_inventory, [], [my_function], [], []);

... Interoptopus generates

Language Crate Sample Output
C# (incl. Unity) interoptopus_backend_csharp Interop.cs
C interoptopus_backend_c my_header.h
Python CFFI interoptopus_backend_cpython_cffi reference.py
Your language Write your own backend1 -

1 Create your own backend in just a few hours. No pull request needed. Pinkie promise.

Getting Started 🍼

If you ...


  • explicit, type-safe, single source of truth API definition in Rust,
  • quality-of-life patterns on both sides (e.g., options, slices, services, ...)
  • minimal on dependencies, build time, tooling impact,
  • if your project compiles your bindings should work*cough* (i.e., generated and callable),
  • extensible, multiple backends, easy to support new languages, fully customizable,
  • no scripts needed, cargo build + cargo test can produce and test (if lang installed) generated bindings

Gated behind feature flags, these enable:

  • derive - Proc macros such as ffi_constant, ffi_function, ffi_type.
  • testing - Functions to test generated Python, C#, C from Unit tests.
  • serde - Serde attributes on internal types.
  • log - Invoke log on FFI errors (you still need actual logger).

Supported Rust Constructs

See the reference project; it lists all supported constructs including:

  • functions (extern "C" functions and delegates)
  • types (primitives, composite, enums (numeric only), opaques, references, pointers, ...)
  • constants (primitive constants; results of const evaluation)
  • patterns (ASCII pointers, options, slices, classes, ...)

As a rule of thumb we recommend to be slightly conservative with your signatures and always "think C", since other languages don't track lifetimes well and it's is easy to accidentally pass an outlived pointer or doubly alias a &mut X on reentrant functions.

Performance 🏁

Generated low-level bindings should be "zero cost" w.r.t. hand-crafted bindings for that language. However, even hand-crafted bindings have an inherent, language-specific cost. For C# that cost can be almost 0, for Python CFFI it can be high. Patterns and convenience helpers might add additional overhead.

If you need API design guidance the following (wip) C# call-cost table🔥 can help.


  • v0.3 - Better compatibility with generics.
  • v0.2 - Introduced "patterns"; produces generally working interop for C#.
  • v0.1 - Has generated C#, C, Python-CFFI bindings at least once.



PRs are welcome.

  • Bug fixes can be submitted directly. Major changes should be filed as issues first.
  • Anything that makes previously working bindings change behavior or stop compiling is a major change;
  • This doesn't mean we're opposed to breaking stuff just that we'd like to talk about it before it happens.
  • New features or patterns must be materialized in the reference project and accompanied by an interop test (i.e., a backend test running C# / Python against a DLL invoking that code) in at least one included backend.