October 2018 - Boost - lists.preview.boost.org

Mailman upgrade
by Brad Johnson 27 Oct '18

27 Oct '18

Happy Late October all. Just a quick notification that mailman upgraded from 2.1.26 -> 2.1.29 at 27-Oct-2018 02:50 UTC. Release notes for 2.1.27, 2.1.28, and 2.1.29: https://launchpad.net/mailman/2.1/2.1.27 https://launchpad.net/mailman/2.1/2.1.28 https://launchpad.net/mailman/2.1/2.1.29 Sanity checks on test mailing list shows mail is still flowing and archiving. Any questions or concerns, please let me know at this address or sysadmin(a)boost.org. Thanks, -- Brad Johnson Ciere Consulting 916.877.6030 brad.johnson(a)ciere.com ciere.com

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[parameter_python] Merge to master
by Edward Diener 26 Oct '18

26 Oct '18

I would like to merge parameter_python to 'master' from 'develop'. Does anybody see anything wrong with this ? This fixes using Python 3+ with parameter as well as Python 2+, among other things.

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Library devs only: Boost v2.x distro design questions
by Niall Douglas 26 Oct '18

26 Oct '18

Splitting this off from the other thread, can I get feedback from Boost library maintainers ONLY. Not users, not non-maintainers. Q0: Are you willing to do the work to adapt your library for any Boost v2.x distro if it were to happen? Q1: Would you prefer a new, separate Boost v2.x distro in parallel to the v1.x distro, or to keep everything within one v1.x distro? Q2: Would you be intending to keep your library inside Boost v1.x, move it exclusively to Boost v2.x, or have it exist in both Boost v1.x and v2.x but with different defaults configured? Also, would the version in v1.x be hard forked from any v2.x edition i.e. the v1.x edition would get orphaned? Q3: What C++ standard should Boost v2.x's master build system be defaulted to? C++ 11, 14, 17 or 20? Q4: Should Boost v2.x use a boost2 namespace, or namespace boost { inline namespace v2 { }}? (This affects whether Boost v2 and v1 editions of your library can be used within the same translation unit) Q5: What master buildsystem should Boost v2.x use? Boost.Build, cmake, Build2, something else? Q6: Should Boost v2.x's libraries auto integrate individually into some package manager? If so, which ones do you intend to support? Q7: Should Boost v2.x have official release versions done by release managers, or should it be a rolling release of "whatever last passed the CI @ 100%"? Note that you can have this, and have official release versions of "especially known good" editions too. Q8: Should Boost v2.x use a local HTML server to serve documentation, and the static HTML docs be dispensed with as a requirement? Q9: What are your feelings towards the use of Python to script infrastructure and tooling in any Boost v2.x? For example, Python to run a local HTML server to serve documentation locally, or Python to build a release etc Q10: What parts of core Boost are you utterly dependent upon, and would absolutely need ported to any Boost v2.x as no STL alternatives exist? I could go on, but let's stop there for now. Niall

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[histogram] Objections against switch to C++14?
by Hans Dembinski 26 Oct '18

26 Oct '18

Dear reviewers of boost.histogram, thank you again for your reviews. I am currently working on the issues raised during the review and some of the requested features would be easier to implement when the library standard is raised from C++11 to C++14. This only affects the implementation side, not the user side. It would make my life easier and the implementation code more readable, because I can emulate `if constexpr` using in-place generic lambdas instead of out-of-place functors in the detail namespace. To make the library more user-friendly, I have to do more and more of these emulated `if constexpr`. Do you object against raising the requirement from C++11 to C++14 for the implementation of boost.histogram? Best regards, Hans

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[smart_ptr] sharable_ptr any interest
by Marc Pawlowsky 26 Oct '18

26 Oct '18

I am working on a idea for a smart pointer called sharable_ptr. A cross between a unique_ptr and a shared_ptr. A sharable pointer has a single definite owner like a unique_ptr, and can be shared to other users similar to shared_ptr as a borrowed_ptr. However unlike a shared_ptr it is an error if the contents of the sharable_ptr go out of scope, by destruction or being reset or assigned, if there are still instances of a borrowed_ptr that reference it. The work is in its infancy at https://github.com/marcpawl/smart_ptr/tree/feature/leased_ptr with the documentation at https://github.com/marcpawl/smart_ptr/blob/feature/leased_ptr/doc/smart_ptr… >From the documentation: Motivation sharable_ptr, and its cohorts: sharable_ref, borrowed_ptr, and borrowed_ref are to help close the raw dangling pointer problem. Along with unique_ptr and shared_ptr, the number of C++ objects that will retain a raw pointer can be reduced. It will allow for easier reasoning of the lifespan of objects, and help catch errors where an object is referenced after it no longer should be. <https://github.com/marcpawl/smart_ptr/blob/feature/leased_ptr/doc/smart_ptr…> Analogy Marc owns a cottage on the lake and is willing to share it with his friends and family. He tells them to drop by anytime they want, even when he is not there. Amanda uses the cottage on a regular basis. Amanda also lets her friend Ava use it. Unfortunately due to a change in financial circumstances Marc has to sell the cottage. At this point neither Marc nor Amanda may use the cottage any more. In C++ terms, Marc has a sharable_ptr<Cottage>. When Amanda is at the cottage she has a borrowed_ptr<Cottage>, which she destroys when she leaves the cottage. When Amanda lets Ava use the cottage Ava gets a copy of the borrowed_ptr. Amanda and Ava must destroy their pointers prior to Marc releasing his. It would be an error for Amanda or Ava to retain a borrowed_ptr to the cottage even if she does not use it. Equivalent to retaining a copy of the keys. ## Alternatives Instead of using `sharable_ptr` and `borrowed_ptr`, you could use `shared_ptr` and `weak_ptr`. The error detection for a dangling pointer gets pushed to when the `weak_ptr` is locked to a `shared_ptr`, instead of when the owned object is freed. A possible advantage is that if the `weak_ptr` is not used then there is no error. The disadvantage is the code may have progressed quite a way before it is realized the referenced object no longer exists. Is there interest in this idea, should I keep working on it? I have so far only been working on Mac clang basement:smart_ptr marcpawl$ clang -v Apple LLVM version 10.0.0 (clang-1000.10.44.2) Target: x86_64-apple-darwin17.7.0 Thread model: posix Thanks Marc Pawlowsky

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interest in a flag library
by Marc Pawlowsky 26 Oct '18

26 Oct '18

You should take a look at https://www.youtube.com/watch?v=1fwbG5TyI18 CPPCON 2018 session https://cppcon2018.sched.com/event/FnKQ/avoiding-disasters-with-strongly-ty… Arno Lepisk <https://cppcon2018.sched.com/speaker/arno_lepisk> Avoiding Disasters with Strongly Typed C++ I think the technique he describes is what you are looking for.

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[c++ question] detecting reference to temporaries
by Raffi Enficiaud 25 Oct '18

25 Oct '18

I have a stupid question related to a bug in boost.test. A piece of code is doing something like: const value& get() { return *internal_iterator; // can be a ref or not to value or another type } The fix is trivial, *but* I want to test it. Is there any technique that would let me test for reference to temporaries? The only option I see would be to promote compiler warnings into error, but maybe there is something there? Thanks, Raffi (complete example here: https://github.com/boostorg/test/blob/90d577a620e008417af79f5caa25e701eef95… )

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[boost.random] Library maintenance
by Nikita Kniazev 25 Oct '18

25 Oct '18

Random library has multiple PRs that hang for a long time already. Some of them address warnings that poisons its usage and maintenance of other libraries. Please consider placing Random under CMT. https://github.com/boostorg/random/pull/35 https://github.com/boostorg/random/pull/26 https://github.com/boostorg/random/pull/31

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Re: [boost] [c++ question] detecting reference to temporaries
by Nikita Kniazev 25 Oct '18

25 Oct '18

> Is there any technique that would let me test for reference to > temporaries? The only option I see would be to promote compiler warnings > into error, but maybe there is something there? AddressSanitizer with -fsanitize-address-use-after-scope https://github.com/google/sanitizers/wiki/AddressSanitizerUseAfterScope

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Boost 2 and build2
by Boris Kolpackov 25 Oct '18

25 Oct '18

I've noticed the discussion on Boost 2 where build2 was mentioned as one of the potential build systems. So I wanted to say that we would be happy to help on our side with any questions, missing features (like exporting targets in a CMake-compatible manner, as mentioned by Niall), etc. Also a couple of additional points about build2 that I think could be relevant to Boost 2 (or 1): 1. It is currently the only build system that I am aware of that has support for C++ modules (currently TS but we are tracking the standardization/implementation progress closely; see [1] for details). Now that modules are likely to be in C++20 I think this should be at least a consideration for Boost 2. 2. We have a public CI service[2] for open source project that I think could be quite useful to Boost. It might not currently be as extensive as Boost's (see [3] for the currently offered build configurations) but we are continuously expanding it plus Boost can run its own build machines with additional configurations. 3. build2 comes with a package manager[4] and Boost could take advantage of that by either publishing to cppget.org or running its own package repository (or both). I am happy to answer any questions here (if appropriate, of course), on the build2 mailing list[5], or on the #build2 slack channel[6]. [1] https://build2.org/build2/doc/build2-build-system-manual.xhtml#cxx-modules [2] https://ci.cppget.org [3] https://ci.cppget.org/?build-configs [4] https://build2.org/build2-toolchain/doc/build2-toolchain-intro.xhtml#guide-… [5] https://lists.build2.org/ [6] https://cpplang.slack.com/app_redirect?channel=build2

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