Re: Proposal: A block between "try" and "catch".

From:
peter koch larsen <peter.koch.larsen@gmail.com>
Newsgroups:
comp.lang.c++.moderated
Date:
Fri, 6 Jun 2008 16:09:45 CST
Message-ID:
<57ac0d1b-a0f2-4344-8856-0a0e5eaaeb81@y21g2000hsf.googlegroups.com>
On 6 Jun., 06:22, "Adam H. Peterson" <alpha.eta...@gmail.com> wrote:

On Jun 5, 4:55 pm, peter koch larsen <peter.koch.lar...@gmail.com>
wrote:

What is wrong with:


[snip wrong solution]

This handles exactly what you want to handle.


Actually, it handles exactly the opposite of what I want to handle.
The exception from the construction of ob will propagate, and the
exception from do_something_else will not.


Of course, I misread your original post. No wonder I was slightly
surprised by your question. Morale: never post when you're tired.

I believe this is obfuscation. A catch block that sometimes does not
catch anything is not something I would recommend.


Most catch blocks sometimes don't catch anything -- if that exception
isn't thrown, or is thrown outside the try block. And in a more
direct parallel, a catch block won't catch something that's thrown
within another catch block (even an earlier catch block for the same
try block). That was the semantic I was trying to parallel. But, I'm
not married to the syntax. I'm just looking for some solution to the
expression of the problem.


I still don't like your syntax. Probably you already tried something
like:

try {
      bool ob_created(false);
      Object ob("data"); // May throw range_error
      ob_created = true;

      // This may also throw range_error,
      // but I don't want to catch this one
      do_something_else(ob, "other data");

} catch (range_error e) {
       if (ob_created)
           throw;

      // handle the failed construction of ob.
}

It is not to elegant, but does the job. If the above gets to tiresome,
perhaps Barbatis boost::optional proposal is better?

/Peter

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