#swig #java #jni #ffi #cxx


Tool for connecting libraries written in Rust with other languages

5 releases

0.6.0-pre5 Jul 27, 2020
0.6.0-pre4 Jul 21, 2020
0.6.0-pre3 Jun 30, 2020
0.6.0-pre1 Jun 29, 2020

#115 in FFI

31 downloads per month


21K SLoC

flapigen Build Status License Rust Documentation

Tool for connecting programs or libraries written in Rust with other languages. Foreign language api generator - flapigen. Former name rust_swig was changed to not confuse with swig. Currently implemented support for C++ and Java, but you can write support for any language of your choice. For an instruction how to integrate flapigen with your project look here.

Suppose you have the following Rust code:

struct Foo {
    data: i32

impl Foo {
    fn new(val: i32) -> Foo {
        Foo{data: val}

    fn f(&self, a: i32, b: i32) -> i32 {
        self.data + a + b

    fn set_field(&mut self, v: i32) {
        self.data = v;

fn f2(a: i32) -> i32 {
    a * 2

and you want to write in Java something like this:

Foo foo = new Foo(5);
int res = foo.f(1, 2);
assert res == 8;

or in C++ something like this:

Foo foo(5);
int res = foo.f(1, 2);
assert(res == 8);

In order to implement it flapigen suggests the following functionality, in Rust project you write (in Rust language):

foreign_class!(class Foo {
    self_type Foo;
    constructor Foo::new(_: i32) -> Foo;
    fn Foo::set_field(&mut self, _: i32);
    fn Foo::f(&self, _: i32, _: i32) -> i32;
    fn f2(_: i32) -> i32;

and that's all, as a result flapigen generates JNI wrappers for Rust functions and Java code to call these JNI functions or generates C compatible wrappers in case of C++ and C++ code to call these C functions.

Users Guide

📚 Read the flapigen users guide here! 📚


~50K SLoC