🚀 go-pugleaf

In article <42q53c$9v9@news0.rain.rg.net>, Paul Long <plong@perf.com> writes:
>volpe@bart.crd.ge.com (Christopher R. Volpe) wrote:
>[snip:the dead horse that we are beating]
>>Silly contrived example using multiple returns:
>>
>>void manipulate_the_windows(Window *top)
>>{
>>  Window *A, *B, *C;
>>
>>  if (top == NULL) {
>>	return;
>>  }
>>
>>  do_something_with_window(top);
>>  A = get_subwindow(top);
>>  if (A == NULL) {
>>	return;
>>  }
>>
>>  do_something_different_with_window(A);
>>  B = get_subwindow(A);
>>  if (B == NULL) {
>>	return;
>>  }
>>
>>  do_something_with_window(B);
>>  C = get_subwindow(B);
>>  if (C == NULL) {
>>	return;
>>  }
>>
>>  /* All windows I'm looking for are good, so do it */
>>  do_something_weird_with_four_windows(top,A,B,C);
>> 
>>  return; /* Omit this or not as a matter of taste */
>>}
>
>
>Silly contrived example using one (implicit) return path:
>
>void manipulate_the_windows(Window *top)
>{
>  Window *A, *B, *C;
>
>  if (top != NULL) {
>    do_something_with_window(top);
>    A = get_subwindow(top);
>
>    if (A != NULL) {
>      do_something_different_with_window(A);
>      B = get_subwindow(A);
>
>      if (B != NULL) {
>        do_something_with_window(B);
>        C = get_subwindow(B);
>
>        if (C != NULL) {
>          /* All windows I'm looking for are good, so do it */
>          do_something_weird_with_four_windows(top,A,B,C);
>        }
>      }
>    }
>  }
>}

Exactly. Now which is easier to read? And which is easier to modify if you
decide you need to check for some other fatal error immediately after
do_something_different_with_window(A)?

Suppose I want the program to print out appropriate error messages? My 
program becomes:

void manipulate_the_windows(Window *top)
{
  Window *A, *B, *C;

  if (top == NULL) {
	printf("Error: Top is NULL\n");
	return;
  }

  do_something_with_window(top);
  A = get_subwindow(top);
  if (A == NULL) {
	printf("Error: A is NULL\n");
	return;
  }

  do_something_different_with_window(A);
  B = get_subwindow(A);
  if (B == NULL) {
	printf("Error: B is NULL\n");
	return;
  }

  do_something_with_window(B);
  C = get_subwindow(B);
  if (C == NULL) {
	printf("Error: C is NULL\n");
	return;
  }

  /* All windows I'm looking for are good, so do it */
  do_something_weird_with_four_windows(top,A,B,C);
}

What happens to your program?

void manipulate_the_windows(Window *top)
{
  Window *A, *B, *C;

  if (top != NULL) {
    do_something_with_window(top);
    A = get_subwindow(top);

    if (A != NULL) {
      do_something_different_with_window(A);
      B = get_subwindow(A);

      if (B != NULL) {
        do_something_with_window(B);
        C = get_subwindow(B);

        if (C != NULL) {
          /* All windows I'm looking for are good, so do it */
          do_something_weird_with_four_windows(top,A,B,C);
        }
	else
        {
          printf("Error: C is NULL\n");
        }
      }
      else
      {
        printf("Error: B is NULL\n");
      }
    }
    else
    {
      printf("Error: A is NULL\n");
    }
  }
  else 
  {
    printf("Error: Top is NULL\n");
  }
}

Notice how the diagnostics grow further and further away from the test which
causes them to be produced? This is what I find difficult to follow. I don't
know about you, but I've shot myself in the foot on more than one occasion as
a result of having one too many or one too few closing braces deeply nested. I
find it much easier to follow code that doesn't have five levels of
indentation.  

--

Chris Volpe				Phone: (518) 387-7766 (Dial Comm 8*833
GE Corporate R&D			Fax:   (518) 387-6560
PO Box 8, Schenectady, NY 12301		Email: volpecr@crd.ge.com