druntime function to query whether any exception is "in flight"

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On Wednesday, 21 October 2020 at 06:22:28 UTC, Petar Kirov 
[ZombineDev] wrote:
> On Tuesday, 20 October 2020 at 17:45:19 UTC, Andrei 
> Alexandrescu wrote:
>> On 10/20/20 11:23 AM, Adam D. Ruppe wrote:
>>> On Tuesday, 20 October 2020 at 15:16:33 UTC, Andrei 
>>> Alexandrescu wrote:
>>>> One change please - can you have it return the current 
>>>> exception as a Throwable (and null if no exception in 
>>>> flight)?
>>> 
>>> 
>>> and prolly at least document that it shouldn't let the 
>>> reference escape cuz otherwise it complicates memory freeing 
>>> of the exception.
>>> 
>>> basically it would be a borrowed reference. again at least 
>>> just documented, not necessarily enforced, but people should 
>>> be aware escaping it is UB.
>>
>> Nice.
>>
>> extern(C) scope(Throwable) _d_eh_getExceptionInFlight();
>
> onlineapp.d(1): Error: declaration expected, not `(`
>
> extern(C) scope Throwable _d_eh_getExceptionInFlight();
>
> onlineapp.d(1): Error: function 
> `onlineapp._d_eh_getExceptionInFlight` functions cannot be 
> `scope`
>
>
> Slightly off-topic: Unfortunately `scope` is a parameter 
> storage class and not a type qualifier (which is probably the 
> biggest point of contention regarding dip1000) so you can't 
> express what you meant above.
>
> This has certain issues:
> * it makes expressing certain code patterns that should be safe 
> impossible in @safe code (which are e.g. safe in Rust)
> * it makes some holes in @safe (both language and library) hard 
> to fix. See e.g.: https://issues.dlang.org/show_bug.cgi?id=17764
> * doesn't help with concurrency safety issues, like these 
> proposals:
>   * https://forum.dlang.org/post/k831b6$1368$1@digitalmars.com
>   * 
> https://forum.dlang.org/post/kluaojijixhwigoujeip@forum.dlang.org

Related:
https://forum.dlang.org/thread/zayyoiupftrvbummxabk@forum.dlang.org