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OCaml C++ FFI Generator

This project is a pre-pre-pre-pre alpha release of a C++ foreign-function-interface generator for Ocaml. Please use at your own risk.

Installation

This library requires ppx_sexp_conv, pcre, sexplib, cmdliner packages. The easiest way to build is to have installed the opam package manager; then it suffices to run:

opam install ppx_deriving ppx_sexp_conv sexplib cmdliner pcre ounit
make all install

An example of the use of this tool can be found in the ocaml-rocksdb library.

Why do we need another FFI generator?

The first and most important question you ought to be asking yourself as a reader is

Why do we need another FFI Generator for Ocaml?  Isn't Camlidl enough?  What about Ctypes?

This is a very fair question, and I can only answer it by telling you my reasons for writing this tool. YMMV, and I surely would suggest that you strongly consider using one of the above-mentioned tools, before considering this one.

Reasons for using this tool instead of others.

  1. What about CamlIDL? I've been a longtime user of CamlIDL. It's great for C code, when the types are pretty well-behaved and don't have complex structures requiring a lot of allocation/deallocation. And it doesn't deal at all with C++.

  2. What about CTypes? This tool's genesis is in my frustration with Ctypes. Ctypes doesn't deal with C++ either. But originally, I was using the orocksdb library, and while it worked well, I needed to extend it. orocksdb uses Ctypes to interface to the Rocksdb C API, and the new operations I wanted to add were complex. Ctypes is complex to understand, and while I'm a long-time Caml-Light/Ocaml programmer, I didn't relish the thought of figuring out how to allocate/manage/free C memory from Ocaml code. It seemed really complicated.

  3. C++'s STL is a great fit for Ocaml This is the real reason for this project: I've been programming C++ for a number of years, and the STL types (std::string, std::vector, etc) are a great fit for Ocaml's type-constructors, and the memory-ownership semantics of those types match well with Ocaml. So it seemed to me that one could easily generate the type-directed translation code needed to convert complex data-types in C++ to/from ML.

Reasons to NOT use this tool

  1. The code to which you wish to interface is not in C++. This should be obvious. This tool only works for C++.

  2. The C++ code you wish to interface to does not follow the Google C++ Style Guide, or uses a lot of types that do not follow C++ STL conventions. This tool leverages the memory-ownership rules and semantics of the C++ STL, as codified in Google's style guide.

License

This code is released under an Apache 2.0 license .