CL-CXX - Common Lisp wrappers for C++

This library provides an interface to C++ from lisp. It was inspired by Julia's libcxxwrap.

Prerequisites

• CLCXX is installed

Installation

Clone into home/common-lisp directory. Then asdf:test-system "cxx"

Supported Types

• Fundamental types
• Pointers
• Classes can add public members and functions
• POD
• functions, std::function and lambda

Type Conversion

C++ type	Lisp cffi type	Allocation/copy
fundamental	same	copy value
POD struct	same	copy value
std::string	:string	allocate c string
const char*	:string	allocate c string
reference	:pointer	copy pointer address
class	:pointer	allocate class object

for allocated memory a finalizer is defined for these objects.

A Small Example

First you will need to create a C++ glue library that CFF will use when calling C++ functions from Lisp. Compile the code below as a shared library say, libtest.so or libtest.dylib. The commands to do this will vary by compiler and operating system. For testing, it is always good to put the library in the same directory as the lisp code, and ensure that you set the current working directory in your Lisp image. CFFI can take some fiddling to find all the dependencies. This is not unique to this project, all Lisp C/C++ bindings with CFFI have the same requirements.

The C++ Side of the Equation

#include <string>
#include "clcxx/clcxx.hpp"

std::string greet() { return "Hello, World"; }
int Int(int x) { return x + 100; }
float Float(float y) { return y + 100.34; }
auto gr(std::complex<float> x) { return x; }
std::string hi(char* s) { return std::string("hi, " + std::string(s)); }
void ref_int(int& x) { x += 30; }
void ref_class(xx& x) { x.y = 1000000; }
class xx {
 public:
  xx(int xx, int yy) : y(yy), x(xx) {}
  std::string greet() { return "Hello, World"; }
  int y;
  int x;
};

CLCXX_PACKAGE TEST(clcxx::Package& pack) {
  pack.defun("hi", &hi);
  pack.defun("test-int", F_PTR(&Int));
  pack.defun("greet", F_PTR(&greet));
  pack.defun("test-float", F_PTR(&Float));
  pack.defun("test-complex", F_PTR(&gr));
  pack.defun("ref-int", F_PTR(&ref_int));
  pack.defun("ref-class", F_PTR(&ref_class));
  pack.defclass<xx, false>("xx")
      .member("y", &xx::y)
      .defmethod("foo", F_PTR(&xx::greet))
      .defmethod("foo.x", F_PTR([](xx x){return x.x;}))
      .constructor<int, int>(); // could be .constructor<int, int>("make-my-xx-class"); 
}

The Lisp Side of Things

You should walk through the commands below in the REPL to get an idea of how the bindings work. Before you start, ensure you have the dependencies loaded:

(ql:quickload "cffi")
(ql:quickload "cxx")

(defpackage cxx/test
  (:use :cl))
(in-package :cxx/test)

;;; Change the pathname to match that of your system.
(pushnew (merge-pathnames #p"ros/lisp-demo/lib/" (user-homedir-pathname))
         cffi:*foreign-library-directories*
         :test #'equal)

(cffi:define-foreign-library my-lib
  (t (:default "libtest")))

(cffi:use-foreign-library my-lib)

(cxx:init)

(cxx:add-package "TEST" "TEST")

(test:greet)

(test:hi "Cxx")

Loading C++ Class

To create a C++ class you should have the following:

• C++

class A {
 public:
  A(int A, int yy) : y(yy), x(A) {}
  int y;
  int x;
};
CLCXX_PACKAGE class(clcxx::Package& pack) {
pack.defclass<A, false>("A")
      .constructor<int, int>("create-my-A")
      .member("y", &A::y)
      .member("x", &A::x);
}

• lisp

(defvar my-a-class (class:create-my-A 10 20))

Usage

See test files or the cl-cxx-eigen project for further examples.

Architecture

• CLCXX is used to expose C++ function/lambda/member_function/overloaded_function to C function pointer that lisp cffi would call.C++ code is compiled into a shared library --for internals see CLCXX--.

The following steps are expected by this package:

• load C++ shared library (cffi:use-foreign-library my-lib).
• call (cxx:init): this function calls clcxx_init(void (*error_handler)(char *), void (*reg_data_callback)(clcxx::MetaData *, uint8_t)).
  • error_handler is used to make C++ call lisp error function.
  • reg_data_callback is used to pass C function pointer, function paramters types and return type to lisp for registering lisp cffi function.
• call (cxx:add-package "TEST" "TEST"): this function calls register_package(const char *cl_pack,void (*regfunc)(clcxx::Package &)).
  • cl_pack is the lisp package name.
  • regfunc is the function name in the compiled C++ shared library CLCXX_PACKAGE regfunc(clcxx::Package& pack).
• C++ package functions are avialable.

NOTE

Tested on:

• SBCL 1.4.5 on debian
• CCL 1.12 on MacOS 10.13.6

TODO

• test functions
• code refactor
• global objects sometimes don't call its finalizers!
• classes
• references
• Smart pointers
• Tuple
• benchmark

Alternative

• CL-CXX-JIT is a new project to make the process easier example: (from '("<cmath>") 'import '("static_cast<double(*)(double)>(std::sin)" . "cpp-sin")), then can be called with(cpp-sin 0d0). CL-CXX-JIT package recompiles c++ files every time, so can be used for quick experimentations, then use cl-cxx.

Copyright

Copyright (c) 2018 Islam Omar (io1131@fayoum.edu.eg)

License

Licensed under the MIT License.