On Wed, 30 May 2012 05:32:00 -0400, Don Clugston <d...@nospam.com> wrote:
On 30/05/12 10:40, Jonathan M Davis wrote:
On Wednesday, May 30, 2012 10:26:36 deadalnix wrote:
The fact that error don't trigger scope and everything is nonsensial.
If an Error is truly unrecoverable (as they're generally supposed to
be), then
what does it matter? Something fatal occured in your program, so it
terminates. Because it's an Error, you can get a stack trace and report
something before the program actually terminates, but continuing
execution
after an Error is considered to be truly _bad_ idea, so in general, why
does
it matter whether scope statements, finally blocks, or destructors get
executed? It's only rarer cases where you're trying to do something like
create a unit test framework on top of assert that you would need to
catch an
Error, and that's questionable enough as it is. In normal program
execution,
an error is fatal, so cleanup is irrelevant and even potentially
dangerous,
because your program is already in an invalid state.
That's true for things like segfaults, but in the case of an
AssertError, there's no reason to believe that cleanup would cause any
damage.
There's also no reason to assume that orderly cleanup *doesn't* cause any
damage. In fact, it's not reasonable to assume *anything*.
Which is the point. If you want to recover from an error, you have to do
it manually. It should be doable, but the default handling should not
need to be defined (i.e. implementations should be free to do whatever
they want).
But there is no reasonable *default* for handling an error that the
runtime can assume.
I'd classify errors/exceptions into three categories:
1. corruption/segfault -- not recoverable under any reasonable
circumstances. Special cases exist (such as a custom paging mechanism).
2. program invariant errors (i.e. assert errors) -- Recovery is not
defined by the runtime, so you must do it manually. Any decision the
runtime makes will be arbitrary, and could be wrong.
3. try/catch exceptions -- these are planned for and *expected* to occur
because the program cannot control it's environment. e.g. EOF when none
was expected.
The largest problem with the difference between 2 and 3 is the actual
decision of whether an exceptional case is categorized as 2 or 3 can be
decoupled from the code that decides between them.
For example:
double invert(double x)
{
assertOrEnfoce?(x != 0); // which should it be?
return 1.0/x;
}
case 1:
void main()
{
writeln(invert(0)); // clearly a program error
}
case 2:
int main(string[] args)
{
writeln(invert(to!double(args[1])); // clearly a catchable error
}
I don't know of a good way to solve that...
-Steve
