[]=

static VALUE
rb_fiddle_ptr_aset(int argc, VALUE argv[], VALUE self)
{
    VALUE arg0, arg1, arg2;
    VALUE retval = Qnil;
    size_t offset, len;
    void *mem;
    struct ptr_data *data;

    TypedData_Get_Struct(self, struct ptr_data, &fiddle_ptr_data_type, data);
    if (!data->ptr) rb_raise(rb_eFiddleError, "NULL pointer dereference");
    switch( rb_scan_args(argc, argv, "21", &arg0, &arg1, &arg2) ){
      case 2:
        offset = NUM2ULONG(arg0);
        ((char*)data->ptr)[offset] = NUM2UINT(arg1);
        retval = arg1;
        break;
      case 3:
        offset = NUM2ULONG(arg0);
        len    = NUM2ULONG(arg1);
        if (RB_TYPE_P(arg2, T_STRING)) {
            mem = StringValuePtr(arg2);
        }
        else if( rb_obj_is_kind_of(arg2, rb_cPointer) ){
            mem = rb_fiddle_ptr2cptr(arg2);
        }
        else{
            mem    = NUM2PTR(arg2);
        }
        memcpy((char *)data->ptr + offset, mem, len);
        retval = arg2;
        break;
      default:
        rb_bug("rb_fiddle_ptr_aset()");
    }
    return retval;
}