#+TITLE: cffi-ops
Write CFFI stuff quickly without runtime overhead.
* Introduction
CFFI is powerful, but using its API to write C-style code can sometimes be cumbersome because it requires you to repeatedly pass in types,
unlike the dot operator in C that has some type inference capabilities.

This library provides CFFI with dot operator-like functionality at compile time,
allowing you to write CFFI-related code as simple as C with just a small amount of FFI type declarations.

This library has been tested to work on SBCL, CCL, ECL, ABCL, and CLISP,
and theoretically is portable across implementations that provide ~macroexpand-all~.
* Rules
Here is a comparison table between C syntax:

| C                        | ~cffi-ops~                                                                       |
|--------------------------+--------------------------------------------------------------------------------|
| ~x->y.z~ or ~x->y->z~        | ~(-> x y z)~ (Note that ~x~, ~y~, and ~z~ must be the same symbols used in ~defcstruct~) |
| ~&x->y~                    | ~(& (-> x y))~                                                                   |
| ~*x~                       | ~([] x)~                                                                         |
| ~x[n]~                     | ~([] x n)~                                                                       |
| ~&x[n]~ or ~x + n~           | ~(& ([] x n))~                                                                   |
| ~x.y = z~                  | ~(setf (-> x y) z)~ if ~z~ is a variable                                           |
|                          | ~(csetf (-> x y) z)~ if ~z~ is a CFFI pointer                                      |
| ~A _a, *a = &_a~           | ~(clet ((a (foreign-alloca '(:struct A)))) ...)~                                 |
| ~A *a = malloc(sizeof(A))~ | ~(clet ((a (cffi:foreign-alloc '(:struct A)))) ...)~                             |
| ~A _a = *b, *a = &_a~      | ~(clet ((a ([] b))) ...)~                                                        |
| ~A *a = b~                 | ~(clet ((a b)) ...)~                                                             |

Please note that since it is not possible to directly manipulate C compound types in Lisp,
binding and assignment of compound types require the use of ~clet~ (or ~clet*~) and ~csetf~,
which bind and operate on variables that are CFFI pointers.

And the symbol ~->~ is directly exported from the [[https://github.com/hipeta/arrow-macros][arrow-macros]] package,
so this library is fully compatible with ~arrow-macros~,
which means you can freely use all the macros (including ~->~) provided by ~arrow-macros~ inside or outside of ~clocally~, ~clet~, ~clet*~, or ~csetf~.
* Example
For the following C code:

#+BEGIN_SRC c
  #include <stdlib.h>
  #include <assert.h>

  typedef struct {
    float x;
    float y;
    float z;
  } Vector3;

  typedef struct {
    Vector3 v1;
    Vector3 v2;
    Vector3 v3;  
  } Matrix3;

  void Vector3Add(Vector3 *output, const Vector3 *v1, const Vector3 *v2) {
    output->x = v1->x + v2->x;
    output->y = v1->y + v2->y;
    output->z = v1->z + v2->z;
  }

  int main(int argc, char *argv[]) {
    Matrix3 m1[3];
    m1[0].v1.x = 1.0;
    m1[0].v1.y = 2.0;
    m1[0].v1.z = 3.0;
    Matrix3 m2 = *m1;
    Vector3 *v1 = &m2.v1;
    Vector3 *v2 = malloc(sizeof(Vector3));
    ,*v2 = *v1;
    v2->x = 3.0;
    v2->z = 1.0;
    Vector3Add(v1, v1, v2);
    assert(v1->x == 4.0);
    assert(v1->y == 4.0);
    assert(v1->z == 4.0);
    free(v2);
    return 0;
  }
#+END_SRC

The equivalent Lisp code (written using ~cffi-ops~) is:

#+BEGIN_SRC lisp
  (defpackage cffi-ops-example
    (:use #:cl #:cffi #:cffi-ops))

  (in-package #:cffi-ops-example)

  (defcstruct vector3
    (x :float)
    (y :float)
    (z :float))

  (defcstruct matrix3
    (v1 (:struct vector3))
    (v2 (:struct vector3))
    (v3 (:struct vector3)))

  (defun vector3-add (output v1 v2)
    (clocally
      (declare (ctype (:pointer (:struct vector3)) output v1 v2))
      (setf (-> output x) (+ (-> v1 x) (-> v2 x))
            (-> output y) (+ (-> v1 y) (-> v2 y))
            (-> output z) (+ (-> v1 z) (-> v2 z)))))

  (defun main ()
    (clet ((m1 (foreign-alloca '(:array (:struct matrix3) 3))))
      (setf (-> ([] m1 0) v1 x) 1.0
            (-> ([] m1 0) v1 y) 2.0
            (-> ([] m1 0) v1 z) 3.0)
      (clet* ((m2 ([] m1))
              (v1 (& (-> m2 v1)))
              (v2 (foreign-alloc '(:struct vector3))))
        (csetf ([] v2) ([] v1))
        (setf (-> v2 x) 3.0
              (-> v2 z) 1.0)
        (vector3-add v1 v1 v2)
        (assert (= (-> v1 x) 4.0))
        (assert (= (-> v1 y) 4.0))
        (assert (= (-> v1 z) 4.0))
        (foreign-free v2))))
#+END_SRC

And the equivalent Lisp code (written without using ~cffi-ops~) is:

#+BEGIN_SRC lisp
  (defpackage cffi-example
    (:use #:cl #:cffi))

  (in-package #:cffi-example)

  (defcstruct vector3
    (x :float)
    (y :float)
    (z :float))

  (defcstruct matrix3
    (v1 (:struct vector3))
    (v2 (:struct vector3))
    (v3 (:struct vector3)))

  (declaim (inline memcpy))
  (defcfun "memcpy" :void
    (dest :pointer)
    (src :pointer)
    (n :size))

  (defun vector3-add (output v1 v2)
    (with-foreign-slots (((xout x) (yout y) (zout z)) output (:struct vector3))
      (with-foreign-slots (((x1 x) (y1 y) (z1 z)) v1 (:struct vector3))
        (with-foreign-slots (((x2 x) (y2 y) (z2 z)) v2 (:struct vector3))
          (setf xout (+ x1 x2) yout (+ y1 y2) zout (+ z1 z2))))))

  (defun main ()
    (with-foreign-object (m1 '(:struct matrix3) 3)
      (with-foreign-slots ((x y z)
                           (foreign-slot-pointer
                            (mem-aptr m1 '(:struct matrix3) 0)
                            '(:struct matrix3) 'v1)
                           (:struct vector3))
        (setf x 1.0 y 2.0 z 3.0))
      (with-foreign-object (m2 '(:struct matrix3))
        (memcpy m2 m1 (foreign-type-size '(:struct matrix3)))
        (let ((v1 (foreign-slot-pointer m2 '(:struct matrix3) 'v1))
              (v2 (foreign-alloc '(:struct vector3))))
          (memcpy v2 v1 (foreign-type-size '(:struct vector3)))
          (with-foreign-slots ((x z) v2 (:struct vector3))
            (setf x 3.0 z 1.0))
          (vector3-add v1 v1 v2)
          (with-foreign-slots ((x y z) v1 (:struct vector3))
            (assert (= x 4.0))
            (assert (= y 4.0))
            (assert (= z 4.0)))
          (foreign-free v2)))))
#+END_SRC

Both of them should generate almost equivalent machine code in SBCL and have very similar performance.