Re: [boost] [Hana] Formal review

Subject: Re: [boost] [Hana] Formal review
From: Joel de Guzman (djowel_at_[hidden])
Date: 2015-06-19 18:38:36

On 6/19/15 11:45 PM, charleyb123 . wrote:
>>
>>>> <snip, concern over Hana header-lib-size>
>>
>
>
>>>> 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.
>>
>
>   Louis Dionne respondeth:
>
>> Regarding the "32k header mega library" thing, I'd like to precise that
>> it's
>> not as bad as it seems. First, part of it is just documentation. Second,
>> that's
>> a _real_ 32 kLOC, not a 100 kLOC of dependencies hidden behind a 5 kLOC
>> library.
>> Hana as no dependencies except the <type_traits>, <utility> and <cstddef>
>> headers, which you probably already use anyway. In comparison, including
>> almost
>> any other Boost library will pull in a lot more than 32 kLOCs in
>> dependencies.
>>
>
> This.
>
> For TMP libraries, and particularly for their application in large
> production codebases, I conclude the following pattern tends to hold:  MORE
> IS LESS.
>
> Paraphrased, this would be, "More reusable code in libraries means less
> application-specific code is necessary, so the program is more feature-rich
> and functionality evolves better over time."
>
> Explanation:  A "richer" (well-defined/implemented) library tends to
> provide non-linear value improvements over a "smaller" library.
>
> In large codebases, a "more-complete" library is superior because:
>
[snip]

Well, that sums it up. So let us just agree to disagree. I'll state
my opinion again: less is more in post C++11 TMP. 98% of TMP can be
done in a simple single header file as was done by Peter Dimov and
Eric Niebler with a very simple, straightforward interface. 98% is
more than enough for me. I've written heavy TMP most of my life as
a C++ programmer and the weight of the code was because of the
limitations of C++03 (and prior!).

Let me just make this clear: I am for Hanna's acceptance into boost.
It is cool and well implemented. Many people will find a use for it.
It's just not for me.

Regards,
-- 
Joel de Guzman
http://www.ciere.com
http://boost-spirit.com
http://www.cycfi.com/