Using Ruby Blocks from C with SWIG

Question

I am using SWIG to wrap a C interface in Ruby. Given two structs

typedef struct Vertex {
  int color, discoverd, finished;
  struct Vertex *next;
} Vertex;

typedef struct Graph {
  struct Vertex *vertex;
} Graph;

how can I create a #each method which yields the current vertex, so that I can process it in Ruby. Currently my SWIG interface file contains something like

%extend Graph {
  void each() {
    Vertex *v;

    v = self->vertex;
    while(v) {
      rb_yield(Qnil); // how do I yield a vertex?
      v = v->next;
    }
  }
};

Thanks in advance for your help.

--t6d

Answer 1

One way is convert the vertex to a VALUE with the swig functions. The swig function to wrap the C struct as a ruby/swig object is SWIG_NewPointerObj.

rb_yield(SWIG_NewPointerObj(SWIG_as_voidptr(v), SWIGTYPE_p_Vertex, 0 |  0 ));

SWIG_NewPointerObj/SWIGTYPE_p_* are defined as a macros in the wrapper, so you will need to call the above code from the wrapper (which will happen when you use %extend).