On 4/1/17 2:18 PM, Dmitry Olshansky wrote:
I don't understand what's so difficult to just recognize that "throw new
Exception" creates a unique object that is passed to the exception
handler.
That would be a good possibility: default to creating exceptions as
scope objects, speculating that the catch site may also be scope. If the
catch site does not use scope, then clone into a heap object. This is
speculative, but the cost of cloning is much smaller than the cost of
the allocation so it's not a large loss.
So just mark the exception as unique in the exception handler
code so that catch site is aware of it. Are we just bend on penalizing
programmers for not typing out "scope"?
A catch site that does not use "scope" has more freedom, e.g.:
void fun()
{
static Exception last;
try { ... }
catch (Exception e) { last = e; }
...
}
Such is not possible with a scoped catch. Of course, that's a concern
only if we want to preserve backwards compatibility.
In turn I don't see what adding "scope" to the catch site accomplishes -
you still need to ensure the reference doesn't escape.
You don't. Old code behaves as it always did.
And if it doesn't
escape you may just as well deallocate the exception object.
Ah, so here we're looking at a deduction scheme. Most interesting! First
try to see if "scope" would work (even if not written), and if so just
consider it there.
Such a scheme preserves backward compatibility and leverages the work
done on "scope".
Pardon but I don't see how.
Think again - checks and e.g. deduction (if we add it as you suggested
above) would work pretty much out of the box.
Andrei
