[swift-evolution] Preconditions aborting process in server scenarios [was: Throws? and throws!]

[thislooksfun]

I really hate to bring Java up, but I really do think it got at least one thing right with its error system, namely that one subset of error (namely `RuntimeException`), wouldn't be enforced by the compiler, but could optionally be caught.

Namely, all of the following would then be valid:
// Explicitly declared to throw, but doesn't have to be caught
func runtimeThrowingFunc1() throws {
  throw SubclassOfRuntimeException
}

// Not explicitly declared to throw, and doesn't have to be caught
func runtimeThrowingFunc2() {
  throw SubclassOfRuntimeException
}

// Doesn't have to be caught...
runtimeThrowingFunc1()
do {
  // But you can if you want
  try runtimeThrowingFunc1()
} catch (SubclassOfRuntimeException) {
} catch (RuntimeException) {
}

// Doesn't have to be caught...
runtimeThrowingFunc2()
do {
  // But you can if you want
  try runtimeThrowingFunc2()
} catch (SubclassOfRuntimeException) {
} catch (RuntimeException) {
}
I'm not advocating explicitly for this model, it is based on Java's exception system after all, but it think it's a place to start at the very least.

-thislooksfun (tlf)

> On Jan 16, 2017, at 7:59 PM, Kenny Leung via swift-evolution <swift-evolution at swift.org> wrote:
> 
> It would also enable the testing of fatal conditions, which would be great.
> 
> -Kenny
> 
> 
>> On Jan 16, 2017, at 5:25 PM, Chris Lattner via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> 
>>> On Jan 16, 2017, at 3:57 PM, David Waite via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>> My interpretation is that he was advocating a future where a precondition’s failure killed less than the entire process. Instead, shut down some smaller portion like a thread, actor, or container like .Net's app domains (which for those more familiar with Javascript could be loosely compared with Web Workers).
>>> 
>>> Today - if you wanted a Swift server where overflowing addition didn’t interrupt your service for multiple users, you would need to use something like a pre-fork model (with each request handled by a separate swift process)
>>> 
>>> That's the difference between CLI and desktop apps where the process is providing services for a single user, and a server where it may be providing a service for thousands or millions of users.
>> 
>> Agreed, I’d also really like to see this some day.  It seems like a natural outgrowth of the concurrency model, if it goes the direction of actors.  If you’re interested, I speculated on this direction in this talk:
>> http://researcher.watson.ibm.com/researcher/files/us-lmandel/lattner.pdf <http://researcher.watson.ibm.com/researcher/files/us-lmandel/lattner.pdf>
>> 
>> -Chris
>> 
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> 
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