Re: Proposal for adding C++ level to the meta/libraries.json

From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2020-09-22 14:35:32

On 9/21/20 8:37 PM, Edward Diener via Boost wrote:
> 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++ levels
> 
> 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 
> apparent.
> 
> 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.

One downside of a manual markup is that this information can go out of 
sync. Including due to changes in a dependency of a library. Granted, 
the status quo also has this downside, so it doesn't make things worse. 
But since we're talking about a tag in a JSON document, it would be nice 
if the value could be deduced from dependencies.

> 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'm not sure I understand what "extended" and "required" tags mean. I 
think the most practical tags are the minimal C++ version at which the 
library is minimally useful, and the minimal C++ version at which it is 
fully useful (meaning, the user can use all features of the library).