Re: Opinions on `defer`?

On Wed, 8 Jan 2025 01:21:08 +0100, Janis Papanagnou wrote:

Using heap objects I typically pass the pointers across function
call boundaries. So it doesn't seem to be useful to me if the
'defer' feature controls just block scopes.

Commonly I will have a function that creates some complex data structure,
which involves multiple dynamic allocations of parts of that structure
which are then joined into the whole. If all those allocations succeed,
then I return a single pointer to the whole object; if any of them fail, I
must clean up everything that was partially allocated.

Interfacing to a highly dynamic language (like Python) makes for a lot of
situations like this. Example below ...

/* informational types to indicate that a pointer is “borrowing” its
  reference and doesn’t need to be disposed: */
typedef char
    br_char;
typedef PyObject
    br_PyObject;

static PyObject * discipline_makedict
  (
    PyObject * self,
    PyObject * args
  )
  {
    PyObject * result = NULL;
    PyObject * tempresult = NULL;
    br_PyObject * items;
    const br_char * msg = NULL;
    do /*once*/
      {
        const bool parsed_ok = PyArg_ParseTuple(args, "Os", &items, &msg);
        if (not parsed_ok)
            break;
        if (not PyTuple_Check(items))
          {
            PyErr_SetString(PyExc_TypeError, "expecting a tuple");
            break;
          } /*if*/
        const ssize_t nr_items = PyTuple_Size(items);
        if (PyErr_Occurred())
            break;
        tempresult = PyDict_New();
        if (tempresult == NULL)
            break;
        for (ssize_t i = 0;;)
          {
            if (i == nr_items)
                break;
            br_PyObject * const item = PyTuple_GetItem(items, i);
            if (item == NULL)
                break;
            if (not PyTuple_Check(item) or PyTuple_Size(item) != 2)
              {
                PyErr_SetString(PyExc_TypeError, "expecting a 2-tuple");
                break;
              } /*if*/
            br_PyObject * const first = PyTuple_GetItem(item, 0);
            if (first == NULL)
                break;
            br_PyObject * const second = PyTuple_GetItem(item, 1);
            if (second == NULL)
                break;
            if (PyDict_SetItem(tempresult, first, second) < 0)
                break;
            ++i;
          } /*for*/
        if (PyErr_Occurred())
            break;
      /* all done */
        result = tempresult;
        tempresult = NULL; /* so I don’t dispose of it yet */
      }
    while (false);
    Py_XDECREF(tempresult);
    return
        result;
  } /*discipline_makedict*/