Re: [boost] [review][mp11] Formal review of Mp11

Subject: Re: [boost] [review][mp11] Formal review of Mp11
From: Joaquin M López Muñoz (joaquinlopezmunoz_at_[hidden])
Date: 2017-07-17 11:06:44

El 17/07/2017 a las 12:20, Peter Dimov via Boost escribió:
> Joaquin M López Muñoz wrote:
>> El 17/07/2017 a las 1:06, Peter Dimov via Boost escribió:
>> > > Joaquin M López Muñoz wrote:
>> > >
>> > >> 1.1 I really don't like the mp_ prefix. [...]
>> >
>> > Well... it's also meant to make it possible to move mp11 into std > 
>> without changes. :-)
>>
>> We already have subnamespaces in std (e.g. std::chrono), so your 
>> standardization
>> plan could be realized as s/boost/std.
>
> It could if I wanted to propose std::mp::if_, but I don't. I want to 
> propose std::mp_if.
>
> I know that this makes the library more difficult to use in other 
> Boost libraries where
> there's no convenient place to put the using directive. :-/

As I see it, users of your library can be divided into three targets:

1. Regular users of Boost.
2. Boost authors (like myself).
3. Users of the std library, once this is proposed to the committee, 
accepted and implemented.

My personal opinion is that 1 should be given priority, followed by 2 
and, at a distance, 3.
It is a submission for Boost we're dealing here with. In that light, mp_ 
sounds like noise
to me (also for 3, but this is not a subject for this review).

> [...]
>
> Our disagreement here rests on whether set should be the same as map. 
> I do not view
> them the same at all. Set is a list with an added constraint, but it's 
> still a list, and list-like
> things can be done to it. It's lower level, so order matters. Map is a 
> higher-level
> key-based structure, where order doesn't matter (logically.)

Totally valid point of view. My intuition about mp11::map comes from the 
definition
("a list of lists [...]") and the std::set/std::map analogy. If you want 
to pull readers away
from that mindset you might want to be a little more descriptive about 
what a map is
meant to be / be used for, and/or change the name to something not 
semantically
overloaded like, say, "dictionary".

>> Something more generic can be provided
>>
>>    struct mp_mpl_sequence_folder
>
> It can, but it ties me to MPL, so I've chosen not to provide it.

This can be confined to a dedicated header, so that the rest of Mp11 is 
MPL-free and your
planned std proposal won't be polluted, and you'd be providing a service 
to potential
users willing to migrate from Boost.MPL but wanting to do so in a 
progressive manner.

Joaquín M López Muñoz