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Subject: Re: [std-proposals] count-based for loop
From: Sophia Poirier (spoirier_at_[hidden])
Date: 2019-08-29 16:23:22


Interesting, thanks Andrew. Do you recall and would mind sharing the reasons for its rejection?

thanks,
Sophia

> On Aug 29, 2019, at 10:21 AM, Andrew Tomazos <andrewtomazos_at_[hidden]> wrote:
>
> I plan to target C++23 with it.
>
> I proposed a similar core language feature in 2016 in P0286:
>
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0268r0.pdf <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0268r0.pdf>
>
> but the proposal was rejected.
>
>
> On Fri, Aug 30, 2019 at 2:46 AM Sophia Poirier <spoirier_at_[hidden] <mailto:spoirier_at_[hidden]>> wrote:
> Thanks Andrew, that's a great collection of utilities. Is that a proposal you are working towards submitting? (I note it has no paper number.)
>
> I do prefer to see it language level as I think it is intuitive as I have suggested, plus it is such a basic and fundamental logical operation (and allows serving those who cannot use the STL), however I do recognize there are fewer hurdles to landing library features.
>
> - Sophia
>
>
>> On Aug 28, 2019, at 5:23 AM, Andrew Tomazos <andrewtomazos_at_[hidden] <mailto:andrewtomazos_at_[hidden]>> wrote:
>>
>> See:
>>
>> https://docs.google.com/document/d/1gBdBualdIU1bpgW_El4GT-p0he9Yr7D52xmLmHes5Qo/edit?usp=sharing <https://docs.google.com/document/d/1gBdBualdIU1bpgW_El4GT-p0he9Yr7D52xmLmHes5Qo/edit?usp=sharing>
>>
>> On Wed, Aug 28, 2019 at 3:42 AM Sophia Poirier via Std-Proposals <std-proposals_at_[hidden] <mailto:std-proposals_at_[hidden]>> wrote:
>>> On Aug 27, 2019, at 10:26 AM, Barry Revzin <barry.revzin_at_[hidden] <mailto:barry.revzin_at_[hidden]>> wrote:
>>>
>>> On Tue, Aug 27, 2019, 12:02 PM Sophia Poirier via Std-Proposals <std-proposals_at_[hidden] <mailto:std-proposals_at_[hidden]>> wrote:
>>> Thanks, yes I have that as an alternate example in my longer notes. My understanding is that it still suffers from the type-matching problem as traditional for loops. Your example of:
>>>
>>> for (const auto i : std::views::iota(0, count))
>>>
>>> only works when count is an int. Otherwise, if for example count is uint32_t, it would need to be:
>>>
>>> for (const auto i : std::views::iota(uint32_t{0}, count)
>>> or:
>>> for (const auto i : std::views::iota(0u, count))
>>> or:
>>> for (const auto i : std::views::iota<uint32_t>(0, count))
>>> or:
>>> for (const auto i : std::views::iota<decltype(count)>(0, count))
>>>
>>> or something along those lines, or you will get template instantiation failure compiler error. I think that if std::views::iota had a constructor overload that was simply the second argument (count) with implicit zero start, then it would be a good option. However I believe there is interest to reserve such an overload perhaps for infinite ranges?
>>>
>>> thanks,
>>> Sophia
>>>
>>> This is true. But we can write a helper function to get the correct type of 0 so we don't need the ugliness at point of use:
>>>
>>> template <std::integral T>
>>> auto upto(T n) {
>>> return views::iota(T{0}, n);
>>> }
>>>
>>> We end up with:
>>>
>>> for (const auto i : upto(count))
>>>
>>> Barry
>>
>> This could be the basis of an alternate library proposal, true.
>>
>> - Sophia



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