[cfe-dev] [ clang::Optional ] History Digging

[ThePhD via cfe-dev]

Dear David,

     Thanks for explaining all of that to me! I feel like I'm starting to
come to a close from all the surveying of the optional implementations and
usages thus far. I think there's only one question I have left, though, and
it has to do with the use of T* as a "optional rebind-able reference".

     Has the use of T* for this purpose ever had any problems? I would
imagine that people used to the codebase have gotten used to it, but has it
ever needed explaining or clarification in places about what the raw
pointer's purpose was to a newcomer?

     I ask mostly because I've seen T* used for a -lot- of different
purposes, so I generally get curious if having it as an "optional
rebind-able reference" has ever led to confusion for the other (mis?)uses
attributed to the syntax.

Sincerely,
ThePhD

On Tue, Jul 10, 2018 at 3:17 PM David Blaikie <dblaikie at gmail.com> wrote:

> Hi there,
>
> Source control has most of the history - and in this particular case, it's
> so far back in the earlier days of LLVM/Clang (Optional was originally
> committed to Clang without any pre-commit review that I can see - in r78342
> (git hash d4e5a606c9c64e24c05e5f4610796087e911fb9c)).
>
> It looks like the original version didn't have any particular support for
> references, though it probably would've worked in that initial simple
> version. Since then no one's attempted to add support for references and
> additional complexity of other features (construction from rvalue
> references, etc) without concern for references has broken any incidental
> reference support it may've had.
>
> So I don't think it was some explicit choice not to support it - but a
> lack of need & probably by the time folks (such as myself) were talking
> about whether it should support references, there was enough open
> discussion about the traedoffs/complexities of supporting them (thanks to
> the committee discussions, etc) that there was probably at least a little
> hesitance - likely enough to err on the side of "let's just keep doing
> things the way we have and use raw pointers for 'optional rebindable
> references'".
>
> On Mon, Jul 9, 2018 at 3:49 PM ThePhD via cfe-dev <cfe-dev at lists.llvm.org>
> wrote:
>
>> Dear Clang Developers,
>>
>>      I am trying to do a little bit of history diving. Back in 2010
>> clang::Optional was moved to llvm::Optional, and has since then maintained
>> its current interface with minor fixes / changes here and there.
>>
>>      I was interested in finding out the initial motivation for
>> clang::Optional, and what features it wanted to support. In particular,
>> clang::Optional doesn't feature support for references, and a few other
>> minor things that differ from the dominating optional implementation around
>> the time of its transition and inception: boost::optional. This is one of
>> the only optionals of its time that publicly made its own design decision,
>> before "because the proposal / standard told me so" was a valid reason for
>> doing so.
>>
>>      Does anyone know if clang::Optional's design was discussed at all?
>> Or if there are any archives for said discussion? This is a bit of an
>> archaeology question, but I was hoping I could get answers nonetheless!
>>
>
>> Sincerely,
>> ThePhD
>> _______________________________________________
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>> cfe-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>
>
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