Re: [boost] A possible date for dropping c++03 support

On 8/25/2018 10:42 PM, Mike Dev via Boost wrote:

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-----Original Message----- From: Boost On Behalf Of Edward Diener via Boost Sent: Sunday, August 26, 2018 7:07 AM

On 8/25/2018 1:51 PM, Mike Dev via Boost wrote:

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From the discussion about abi compatibility when the Boost.System library is compiled e.g. in c++03 mode and then included in a c++11 project or vice versa (https://groups.google.com/forum/#!topic/boost-developers- archive/EWG5NVOZo_ g)

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When can we drop C++03 support? :D

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What about the first or second release in 2020 ?

Please define what is meant by "dropping C++03 support

For me it means that

- a contributor can use c++11 language and library features (be it the library maintainer or someone else opening a PR on Github)

There are libraries which work with C++03 on up. If a contributor decides to use a C++11 language or library feature with that library it can no longer work with C++03. I think it should be up to the library maintainer whether a library no longer works with C++03 or not. Otherwise any contributor to a library can decide what C++ standard level that library should support.

- A user (external or internal) may no longer expect a boost library to compile with a compiler not supporting c++11 (and we can have a discussion just which compilers that are) or when he tries to compile it in c++03 language mode (e.g. -std=c++03)

There are plenty of libraries which need some level of support from C++11 on up. The user of that library currently expects that such a library will not work when compiling at the C++03 level. OTOH there are some libraries that will work with C++03 on up. Are you going to tell a user that they should no longer expect to work with such a library at the C++03 level even when it currently works fine at that level ? For what purpose ?

Is that definition precise enough? What other definition did you have in mind (if any)?

I had no definition in mind. Every time someone speaks of Boost "dropping C++03 support" it means whatever that person wants it to mean.

If that is your concern: I would certainly not expect that you start ripping out the guts of an old, battle proven library and replace everything with c++11 features just for the fun of it. However, next time a feature is added or a bug has to be fixed, you no longer have to restrict yourself to c++03.

No library maintainer has to restrict his library to any C++ level. The usual course when upgrading a C++ level is to tell end-users what you intend to do, and then eventually do it in some later Boost release. A new library may be written supporting any C++ standard level that it wants. There is much encouragement in Boost for developers to use a C++ standard level which is useful for whatever they want their library to accomplish. No library is forced to maintain backwards compatibility with the C++03 level if it does not want to do so.

And maybe, over time, some people will contribute patches that simplify / improve a library by replacing some complex c++03 solutions with simpler c++11 solutions when applicable.

Anybody is welcome to do that and a some people have already successfully achieved that goal and had their library accepted into Boost. Boost does not discourage anyone from creating a better version of a library using a more modern C++ level and more modern programming idioms. My objection to the usual Boost "dropping C++03 support" is that there is absolutely no reason for forcing libraries which do support C++03, while being usable at any higher C++ standard level, to do anything. If you think that some library which works with C++03 would be better by using some later C++ standard level feature you can always suggest it and maybe the maintainer will agree with you. But forcing a library to use some idiom of a higher C++ standard level when the library itself has no use for any such an idiom seems pretty foolish to me.

Best

Mike