DIP 1029---Add throw as Function Attribute---Community Review Round 1

[Joseph Rushton Wakeling]

On Tuesday, 14 January 2020 at 17:01:42 UTC, bachmeier wrote:
> Is it a big deal? Maybe not, but it's strange to say "You can 
> invert [random attribute] but no others." "Oh, why is that?" 
> "Because that's all that was in the DIP." It's just sloppy and 
> amateurish to design a language like that.

Yes, but that's not the answer, is it?  The answer to "Why is 
that?" is, possibly among other things, "Because it enables a 
transition path to exceptions being opt-in rather than opt-out."

(Note there is no reason in principle why `nothrow` might not get 
deprecated and dropped if such a transition actually happens, so 
long run we may not end up with the one invertible attribute.)

However, that does raise a good piece of review feedback: is it 
appropriate to introduce this new attribute as a DIP in its own 
right, rather than as a migration path for the nothrow-by-default 
DIP?  Are there use-cases other than the transition that motivate 
the `throw` attribute or make it valuable?

It would be good if the DIP could articulate those arguments if 
they exist -- and if they do not, perhaps its acceptance should 
be made conditional on the (not yet finalized) nothrow-by-default 
DIP.

>> No, you don't need to write up a DIP to counter a DIP, but 
>> comprehensively introducing invertible attributes _will_ need 
>> a DIP.  So if you (or anyone else) thinks that is needed or 
>> valuable, it's worth putting that DIP together.
>
> I don't even know if that's a good idea. All I'm asking for is 
> a sensible argument in favor of adding an inverse of one and 
> only one attribute. It makes absolutely no sense to me to have 
> negation of nothrow but not nogc.

You could look at that from the opposite point of view: what's 
the point in introducing an inverse to a particular attribute 
unless it has a practical motivation beyond the concept that 
"attributes should be invertible"?

FWIW I do think it would be helpful for the DIP to offer a 
response to your question.