• Steve Horne (48/48) Sep 06 2006 I have fallen in love with the scope statement ;-)

Steve Horne <stephenwantshornenospam100 aol.com> writes:

I have fallen in love with the scope statement ;-)

One thing, though. Success vs. failure isn't always a matter of
exception throws. There is a less fatal kind of failure that is often
indicated by a return value.

For instance, if I have a smart iterator with a 'Goto_Next' method, it
will probably return false if it fails. After all, failure isn't all
that exceptional - it happens at the end of every loop. This isn't a
case of 'I should be using exceptions but I'm stupid', it's a case
where exceptions are inappropriate. Readability and maintainability
would get worse if I used them.

Therefore, how about a "scope(return argname)".

For example...


bool Example ()
{
  Save_State ();

  scope(return p)
  {
    if (p) { Discard_Saved_State ();  }
      else { Restore_Saved_State ();  }
  }

  //  Do stuff
}


In a large function, this could save a lot of hassle. Except for one
thing. What if the scope exits some other way.

In the above example, I could just use 'scope(failure)', but what if
the scope statement was in an inner block that could be exited by a
goto or running off the end or whatever?

Do we want a huge selection of 'scope' types so that every possible
exit route can be specified unambiguously?

Well, no, not really. So, how about...


bool Example ()
{
  Save_State ();

  scope(return p)
  {
    if (p) { Discard_Saved_State ();  }
      else { Restore_Saved_State ();  }
  }
  else scope(failure)
  {
    Restore_Saved_State ();
  }
  else
  {
    //  Can't happen here, but I'm sure you get the idea.
  }

  //  Do stuff
}