Re: [boost] [Hana] Formal review

Subject: Re: [boost] [Hana] Formal review
From: Zach Laine (whatwasthataddress_at_[hidden])
Date: 2015-06-19 08:36:00

On Thu, Jun 18, 2015 at 11:35 PM, Joel de Guzman <djowel_at_[hidden]> wrote:

> On 6/19/15 9:12 AM, Louis Dionne wrote:
>
>> Joel de Guzman <djowel <at> gmail.com> writes:
>>
>>
>>> On 6/19/15 3:07 AM, Louis Dionne wrote:
>>>
>>>>   [...]
>>>>
>>>
>>> It's not just about compile time, no. What's more important to me is
>>> the conceptual overhead of using another library to do simple things.
>>> TMP in what were once TMP heavy libraries used to take a significant
>>> amount of code in c++03. Not anymore. Then of course another factor is
>>> minimizing dependencies. The less dependencies the better. Zero is ideal.
>>>
>>
>> I understand your point about minimizing dependencies. However, the same
>> goes
>> for any kind of library, TMP or not. At some point, one must draw a line
>> and
>> accept having external dependencies, or eternally reimplement everything
>> from
>> scratch. I guess you are the only one who can decide where that line
>> should be
>> drawn for your own projects, and that's OK.
>>
>> However, even though you may be content with the ease of writing TMP code
>> in
>> C++14, I think you might be surprised to see how shorter it could be if
>> you
>> used Hana. This is, for example, the case of Zach's Units-BLAS library. It
>> was really quite short with C++14 only, but it was even shorter with Hana.
>> And the code was written with a higher level of abstraction. And in that
>> case, there was even a compile-time speedup over std::tuple + handwritten
>> stuff.
>>
>
> "really quite short" is good enough if the cost is having to depend on
> a "32k header mega library" as David notes. Not to mention having to
> learn another library for me and for all future maintainers. So where
> is the speedup? is it because of std::tuple? If so, why don't you
> decouple your nice tuple implementation and offer it separately?
> Or is it the handwritten stuff? If so why? Why can't Zacc use the
> same tricks that you used in Hana?

I was using effectively the same trick in at least one place, and more ad
hoc ones in others. However, after partially converting to Hana, I could
see a smaller, and thus more maintainable, code base.

As for the "32k header mega library", if it builds faster than the
alternative and I don't need to understand much of that interface anyway, I
find I don't really care.

Zach