Support C++17 code in packages

[rwst]

This is at the moment a ticket for a nonexisting defect, as no standard package uses C++17 code at the moment.

The compiler situation is that C++17 is fully supported by clang++-4 --std=c++17 and g++-7 --std=c++17. So, compiler-wise Sage could support it without raising requirements (currently at g++-4.8) by building g++ if system has g++<7. But for full support libstdc++-gcc7 or libc++-4 is needed too, so g++-7 would be the system requirement.

How much is gcc-7 already in the wild?

Another issue is that with g++-5 I think and clang++-4 the register keyword became deprecated and will be removed with C++17 where it will cause a compiler error. This affects at least Singular and Giac.

Component: build

Issue created by migration from https://trac.sagemath.org/ticket/25255

[jdemeyer]

comment:3

What is this ticket about? The description reads more like a comment than an actual issue to be solved. If the ticket cannot be made more concrete, I suggest closing it. We can always open a ticket whenever a real problem occurs.

[rwst]

comment:4

I have an implementation of commutative matching (needed to fix #25168) in the works that depends on std::optional. This ticket is useful to define the amount of changes needed for it, and for reference. Even if we won't fix #25168 in the near future I'm playing with a project that needs the matching algorithm too, and which I'll release in an experimental branch.

[rwst]

comment:5

Note also that #25168 is more an enhancement as the old behaviour will stay for backward compatibility (in principle it's good to have many different types of matching algorithms).

[rwst]

comment:6

Actually, even Python2.7 (not 3.4) has register in its headers (unicodeobject.h and stringobject.h), and so C++17 code must not include Python.h. Interesting, I opened pynac/pynac#325

[jdemeyer]

comment:7

A Trac ticket is about a concrete issue to be fixed. The stuff you are talking about fits more on a mailing list, wiki or something like that.

[rwst]

comment:8

I agree. I just replaced std::optional usage with that of https://github.com/martinmoene/optional-lite and no longer have a need for C++17.

[videlec]

comment:10

closing positively reviewed duplicates