From: Edward Diener (eldiener_at_[hidden])
Date: 2020-09-22 16:59:36
On 9/22/2020 12:47 PM, Mateusz Loskot via Boost wrote:
> On Tue, 22 Sep 2020 at 18:03, Edward Diener via Boost <boost_at_[hidden]>
>> On 9/22/2020 4:42 AM, Paul A Bristow via Boost wrote:
>>>> -----Original Message-----
>>>> From: Boost <boost-bounces_at_[hidden]> On Behalf Of Edward Diener
>> via Boost
>>>> Sent: 21 September 2020 18:37
>>>> To: boost_at_[hidden]
>>>> Cc: Edward Diener <eldiener_at_[hidden]>
>>>> Subject: [boost] Proposal for adding C++ level to the
>>>> Since we are reviewing Vinnie Falco's JSON library I thought that this
>> would be a good time to present a
>>>> proposal to add information to each Boost library's meta/libraries.json
>> file regarding the level of C++
>>>> standard compliance for that library. This could then be added to each
>> library's visual documentation so
>>>> that end-users would instantly know the C++ standard level they would
>> need to use in order to use a
>>>> Boost library.
>>>> My proposal is to add 3 fields whose data would be the same as the
>> cxxstd allowed values from Boost
>>>> Build, using the first value of each choice ( currently 03, 11, 14, 17,
>> 20 ).
>>>> standard = minimum C++ level for the library extended = same
>> functionality in the library as the
>>>> minimum C++ level but with extended use given higher C++ levels
>> required = new functionality in the
>>>> library above the minimum C++ level which requires given higher C++
>>>> The 'standard' field would be a single value, while the 'extended' or
>> 'required' fields could be more than
>>>> one comma separated value. If you don't like the names for 'standard',
>> 'extended', or 'required' you can
>>>> bikeshed the name, although I think the 'standard' name is pretty well
>>>> The idea is to provide this information in the meta/libraries.json
>> field for each library, so that the end-
>>>> user of the library can immediately know the usability of the library
>> with appropriate C++ standard
>>>> levels of compilation.
>>>> I realize that the line between the 'extended' and 'required' entries,
>> as I have described them, could be
>>>> blurred. The 'standard' field remains the most important. I have long
>> felt that the end-user should not
>>>> have to do any investigation, in code or in documentation, just to
>> determine if a library is usable for his
>>>> C++ standard level of compilation.
>>> I've been muttering about this tricky issue for some time.
>>> For a big and old and still growing library like Boost.Math, the problem
>> is even more difficult.
>>> For many math functions and distributions, C++03 (with C++11
>> numeric_limits) is fine, but as one starts to use newer items, then
>> requirement shift up to needing C++20.
>>> We have recently decided to require a minimum C++11, but that still
>> means that users may find that some components need more.
>>> Predicting the requirements for certain is difficult - I fear in
>> practice, it means 'sucking and seeing' â¹
>>> I have suggested marking each header file with its minimum requirements,
>> but that is messy and doesn't really help the user much.
>>> My ideal is to say 'always use the latest compiler version and highest
>> standard level', but that isn't popular ð
>>> But it is a reason to encourage users to plan to keep updating all their
>> tools - and keep their management on-board with that concept.
>>> So I support Edward's proposal, but caution that it isn't as helpful for
>> some libraries as others.
>> You could tag Math as:
>> standard : 11
>> required : 14, 17, 20
>> It least that tells end-users that C++11 is the minimum level but that
>> some functionality will need C++14, C++17, or C++20.
> I see the idea better now.
> Well, trying to put myself in a library users' shoes,
> seeing `required : 14, 17, 20` raises more questions.
> I'd rather appreciate to see `required: 11`,
> then read a section in the docs explaining that
> "if BOOST_MATH_FANCY_X is defined, then C++14 is required;
> if <x> is included, then C++17 is required"
> and other details clearly, as a guide,
> less obscure than list of numbers.
Using "required" is probably a pretty bad word. Something else might be
better. I am not hung up on terminology, but some word that tells the
end-user that with some higher C++ level(s) more functionality is
available in the library I think would also be useful. Of course this
information is probably available somewhere in the docs, if you can find
it. If my original "extended" and/or "required" is dropped that is fine
with me, but let's at least give the end-user the immediate knowledge of
what C++ minimum level is needed to use a Boost library. Having read
through enough Boost library docs I know that information is often not
provided at all and, if it is there, is hard to find.
Boost list run by bdawes at acm.org, gregod at cs.rpi.edu, cpdaniel at pacbell.net, john at johnmaddock.co.uk