Re: [boost] [Hana] Formal review

On Wed, Jun 10, 2015 at 3:19 AM, Glen Fernandes wrote:

...

- Whether you believe the library should be accepted into Boost * Conditions for acceptance

Yes, I think it should be accepted into Boost. The one condition is that the library works with release versions of at least two different mainstream C++ compilers. More on that later... I understand that we need at least two compilers, but I suppose this should be achieved by the time the library would be ready.

...

You are strongly encouraged to also provide additional information: - What is your evaluation of the library's: * Design

The core technique of combining value and type expressions is solid and makes metaprogramming easier and, as a bonus, improves compilation speeds.

My one question, as I read though the implementation, is "can the core benefits of this library be achived with a simpler 'light' version of this implementation?". While I appreciate the attempt to encode a Haskell-style typeclass hierarchy, I feel like that is not the core competency of hana and should be a separate library and discussion. As it is, this is a 32k header mega library. I'd prefer several small, highly-targeted, highly-composable libraries. I agree that there is the Core of the library and the different types and algorithms. I agree having highly composable types and algorithms, but why do you

Le 17/06/15 21:55, David Sankel a écrit : prefer them split in several libraries? Is because having them on the same library allows the author to take some short cuts that shouldn't be used? Is it because it would be difficult to add other libraries using the Core in a coherent way? Is it because we need time to review each one of the Concepts, types and algorithms? Or, ....

...

* Implementation

The code itself looks to be well structured and well documented.

Unfortunately hana only works with one compiler: clang. While I agree that Boost shouldn't need to support Visual C++ 6.0 anymore, I believe this is going too far in the opposite direction.

The home page states that boost libraries "are intended to be widely useful, and usable across a broad spectrum of applications". I've always interpreted that statement to be in a practical rather than theoretical sense and I don't think hana meets that criteria. The intent of the library is to be widely useful and it will be. Lets

Why? we have discusses this a lot of time and it is up to the library author to state what compilers the library supports. the time do his job.

Many other Boost authors have made heroic efforts to meet that criteria and the reputation of Boost is due, in no small part, to those efforts. You are right that some of us are spending a lot of time trying to cover multiple not conforming compilers and also multiple c++ versions. I believe that this is one of the things slowing the growth of Boost.

I do appreciate the argument that making use of new features encourages compiler implementers to implement then. I maintain, however, that this isn't Boost's job. Boost provides high quality libraries that the every-day Joe C++ developer can benefit from. Lets build them for the every-day Joe C++ developer of tomorrow. Stabilizing a library takes time. But we need that the library be used to learn more. Been in Boost would help to achieve it.

That being my position on the issue, my acceptance vote is conditional on hana supporting at least two released versions of mainstream compilers. Given that gcc support seems pretty close, that shouldn't be hard to achieve.

I agree that at least two compilers seems a minimum. Best, Vicente