[jefbyokyie]

When constructing an object in C, we may need some permanent sub-objects, and some temporary objects.

If we only need permanent sub-objects, then we set those up gradually, and build an error path in reverse order (with gotos or with the arrow pattern); upon success, the sub-objects' ownership is transferred to the new super-object, and the new super-object is returned, just before the error path is reached. Otherwise, the suffix of the error path that corresponds to the successful prefix of the construction path is executed (rollback). This approach cannot be rewritten with "defer" usefully. Normally you'd defer the rollback step for a sub-object immediately after its successful construction step, but this rollback step (= all rollback steps) will run upon successful exit too. So you need a separate flag for neutering all the deferred actions (all deferred actions will have to check the flag).

If we only need temporaries (and no permanent sub-objects), then (first without defer, again) we build the same code structure (using cascading gotos or the arrow pattern), but upon success, we don't return out of the middle of the function; instead, we store the new object outwards, and fall through to the rollback path. IOW, the rollback steps are used (and needed) for the successfully constructed temporaries regardless of function success or failure. This can be directly expressed with "defer"s. The problem is of course that the actual rollback execution order will not be visible in the source code; the compiler will organize it for you. I dislike that.

If we need both temporaries and permanent sub-objects, then we need the same method as with temporaries, except the rollback steps of the permanent sub-objects need to be restricted to the failure case of the function. This means that with either the cascading gotos or the arrow pattern, some teardown steps will be protected with "if"s, dependent on function return value. Not great, but still quite readable. With defer, you'll get a mix of deferred actions some of which are gated with ifs, and some others of which aren't. I find that terrible.

[kubb]

So, you recommend using goto, which indeed is the only available mechanism.

[Someone]

> using goto, which indeed is the only available mechanism.

There are other options, but none of them is better, IMO. You can use nested functions:

    char * p = malloc(10);
    if(p!=0) {
      doTheRealWork(p);
    };
    free(p);

In gcc, doTheRealWork can be a nested function or it you can force them to be inlined.

You can also (more readable than that first alternative, IMO) wrap code in a single-iteration for or while loop and then use break to exit it:

  char *p = null;
  for(int i=0;i==0;i=1) {
    p = malloc(10);
    if(p==0) break;
    …
  }
  free(p);

Both will get uglier if you need to free multiple resources, but will work.