220 2210 <CALJmx62zJd_tZ=XYL7TaSkRN6432SObwH9YS87eLX-h_pMuFYQ@mail.gmail.com> article
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From: Dean Michael Berris <dberris@google.com>
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Subject: Re: optional<T>, one more value or two states
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On Fri, Jan 25, 2013 at 7:07 AM, Fernando Cacciola
<fernando.cacciola@gmail.com> wrote:
> On Thu, Jan 24, 2013 at 12:22 PM, Andrzej Krzemie=F1ski
> <akrzemi1@gmail.com> wrote:
>>
>>
>> W dniu czwartek, 24 stycznia 2013 14:52:22 UTC+1 u=BFytkownik Zhihao Yua=
n
>> napisa=B3:
>>>
>>> On Thu, Jan 24, 2013 at 7:38 AM, Ville Voutilainen
>>> <ville.vo...@gmail.com> wrote:
>>> > I have since cured that problem in my head, there's no 'danger' invol=
ved
>>> > in
>>> > it.
>>>
>>> The danger already shows up.
>>>
>>> Quoting from the proposal:
>>>
>>>   "Such implicit conversions impose some risk of introducing bugs,
>>>    and in fact in order to avoid one such possible bug we had to 'poiso=
n'
>>>    comparisons between optional<T> and T."
>>>
>>> And a carefully specified comparison logic is under discussion.
>>
>>
>> The perceived danger is the opinion of the authors (myself included).
>
> To be honest, it is more that I was sold into it :)
>
> Again if it where entirely up to me, I would put this back in as well
> as mixed comparison operators.
>
> So, it's once a again more of a matter of gauging the probable
> reaction among voting committee members.
>

In my opinion:

- There's a precedent in other languages for a ".get(default_value)".
Why don't we have this for optional instead?

- Why are we forcing pointer semantics on optional? Maybe there's a
different concept here at play.

- As a value type I would be very leery of mixing comparison
operators. Think about how NaN already works in terms of comparison
with float/doubles. It would be surprising to have an optional value
be comparable to a non-optional value.

- Implicit conversion: no confusion here, it's convenient and simple.
If a function takes a optional<T> and you gave it '{}' then you should
expect a default-constructed optional<T> (disengaged). It doesn't make
sense for that optional to be comparable to a non-optional (or
actually even to another optional). The values very well may be
comparable in which case you just compare the values if there are
values to compare.

All I'm reading so far as been "I don't like this" or "I don't prefer
this". I have not seen any sound logical reasoning to say that
anything thus far being presented is illogical or "does not make
sense".

--=20

---=20
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