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#261 in FFI

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21K SLoC

Step Function I/O



Object-oriented binding generator for Rust.


Licensed under the terms of the MIT or Apache v2 licenses at your choice.


  • First, you write your Rust library without thinking about bindings.
  • Then, you write a C FFI to your Rust library, taking into account how object- oriented languages will interact with it. You also make sure to protect as much as possible the interface between your Rust library and the outside C world
  • You define a general object-oriented "schema" that uses the C FFI to interact with your library.
  • You generate the bindings in the target languages using generators that reads the previously defined "schema" and generate easy-to-use, idiomatic and portable code.
  • You write unit tests in the generated languages to make sure everything works as expected.


  • oo-bindgen: main library to build an object-oriented representation of your library.
  • tests: contains an example foo-ffi library with the associated foo-bindings object-oriented library definition. It builds the same library in each supported language. Each language has extensive unit tests written to check that the generated bindings work as expected.

C bindings

A minimal CMakeLists.txt to compile with a library generated by oo-bindgen is the following:

cmake_minimum_required(VERSION 3.8)

project(my_awesome_project LANGUAGES C)

# Find the foo library generated by oo-bindgen
find_package(foo REQUIRED)

# Add your awesome project with a dependency to foo
add_executable(my_awesome_project main.c)
target_link_libraries(my_awesome_project PRIVATE foo)

# Copy the DLL/.so after build
add_custom_command(TARGET my_awesome_project POST_BUILD 
    COMMAND ${CMAKE_COMMAND} -E copy_if_different $<TARGET_FILE:foo> $<TARGET_FILE_DIR:my_awesome_project>

.NET bindings

  • Create a new local NuGet feed. To do this, create an empty directory somewhere then run nuget sources add -Name my-nuget-feed -Source /my-nuget-feed.
  • Add the generated NuGet package to it using nuget add foo.0.1.0.nupkg -Source /my-nuget-feed.
  • In your project, add a dependency to the package. You can do dotnet add MyAwesomeProject package foo or add it using Visual Studio interface. It should add a line in your .csproj like the following: <PackageReference Include="foo" Version="0.1.0" />

Java bindings

  • Install the JAR to your local Maven repository with mvn org.apache.maven.plugins:maven-install-plugin:3.0.0-M1:install-file -D"file=foo-0.1.0.jar"
  • Add the dependency in your project with


~185K SLoC