July 2017 - Boost - lists.boost.org

Mp11 review
by paul 25 Jul '17

25 Jul '17

Hi, this is my review of mp11. Please answer the following questions in your review [4]: > 1. Should Mp11 be accepted into Boost? Please state all conditions > for acceptance explicity. Yes Mp11 should be Accepted. > > 2. What is your evaluation of the design? Very good design overall. I don't know if I really like the `mp_` prefix. Trailing underscores is common in boost, but the mp prefix makes sense for standardization. It uses the `std::integral_constant`, but it might be nice to use another implementation, as that can help make it consistent between C++11 and C++14. Also, providing an integral constant with operators could help improve interoperability with hana-style metaprogramming(which also help interoperate with the Fit library as well). Of course, I don't know if mp11 is right place for it. It seems it would be better to have a separate library for this and the other C+14 features as well. Also why is `mp_with_index` only constexpr on C++14 and higher? > > 3. What is your evaluation of the implementation? The implementation seems to be good and provides competive performance with other metaprogramming libraries, but I do wonder if some of Odin's metaprogramming techniques(such as recursive aliases) can be used to improve the performance as well. > > 4. What is your evaluation of the documentation? Very well documented and organized. > > 5. What is your evaluation of the potential usefulness of the library? I think this library can be very useful for C++11 metaprogramming where I have needed. I don't think it would be as useful for the Fit and Tick library because they still target gcc 4.6, which mp11 doesn't support due to being based around template aliases. > > 6. Did you try to use the library? With what compiler? Did you have > any problems? Yes, I did, and also ran the tests. I tried to run the tests on some configurations that aren't ran in the travis CI(like clang 3.5 with C++14). And all the tests do pass. > > 7. How much effort did you put into your evaluation? A glance? A quick > reading? In-depth study? I spent a couple hours reviewing, and I have implement ad-hoc versions of these in my own libraries as well. Paul

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[review][mp11] Reminder of ongoing formal review
by Bjorn Reese 25 Jul '17

25 Jul '17

The formal review of Mp11 continues until (and including) Monday, July 24th. There have been four formal reviews so far. I would like to ask the Boost community for two favours: 1. Please postpone the discussions about CMake and the future directions of Boost until the formal review has ended. 2. Please review the Mp11 library instead. If you disagree with any of the above, please contact me off-list. Here is the call for review once more: The formal review of Peter Dimov's Mp11 library is scheduled for July 15 - July 24, 2017 [1]. Mp11 is a C++11 metaprogramming library for compile-time manipulation of data structures that contain types. It’s based on template aliases and variadic templates and implements the approach outlined in the article "Simple C++ metaprogramming" [2] and its sequel [3]. These articles are useful background information for the review. * Mp11 aims to make simple usage simple, and to support complex usage without complicating the simple use cases. * Mp11 works on any type-list, whether its own type-list mp_list, or standard type-lists such as std::tuple and std::variant, or user-defined type-lists. * Mp11 works with any meta-function, such as C++11 or Boost type-traits, or user-defined type-traits. Mp11 can be found here: * Documentation: https://rawgit.com/pdimov/mp11/master/doc/html/mp11.html * Source code: https://github.com/pdimov/mp11/tree/master Please answer the following questions in your review [4]: 1. Should Mp11 be accepted into Boost? Please state all conditions for acceptance explicity. 2. What is your evaluation of the design? 3. What is your evaluation of the implementation? 4. What is your evaluation of the documentation? 5. What is your evaluation of the potential usefulness of the library? 6. Did you try to use the library? With what compiler? Did you have any problems? 7. How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? 8. Are you knowledgeable about the problem domain? [1] http://www.boost.org/community/review_schedule.html [2] http://pdimov.com/cpp2/simple_cxx11_metaprogramming.html [3] http://pdimov.com/cpp2/simple_cxx11_metaprogramming_2.html [4] http://www.boost.org/community/reviews.html

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[review][mp11] Review of Mp11 has ended
by Bjorn Reese 25 Jul '17

25 Jul '17

The review of Mp11 has ended with a total of 12 formal reviews (and one pending.) I would like to thank all who have participated in the review, as well as those who agreed to postpone CMake discussions until the end of the review. The review report will be posted in the near future.

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[config] What Feature is this??
by John Maddock 25 Jul '17

25 Jul '17

Folks, I think I'm looking to add a new C++11 defect macro, but don't know what the feature is called, nor can I see a way of detecting it with clang's __has_feature function. The code I want to enable involves function overloading based on a decltype return type as in: auto integrate(args...) -> decltype(expression1); auto integrate(args...) -> decltype(expression2); where expression1 and expression2 are two mutually exclusive options (the conceptual requirements of args means that only one of these 2 will ever be satisfied). This works fine in msvc-14 and later and gcc-4.8 and later, but I don't see any current config macros which cover this case, nor can I figure out what this trick should be called. Alternatively, if anyone has a better way of differentiating between unary and binary functions I'm happy to hear about it ;) Thanks, John. --- This email has been checked for viruses by AVG. http://www.avg.com

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[review][mp11] Formal review of Mp11
by Glen Fernandes 25 Jul '17

25 Jul '17

What follows is my review of the Mp11 library: [Should the library be accepted into Boost?] Yes. I vote for an unconditional ACCEPT. [What is your evaluation of the design?] Excellent. The design where any template can serve as a list, and any template can serve as a meta-function is both elegant and powerful. The additional quoted meta-function support with utilities such as mp_bind, mp_bind_front, and mp_bind_back, addresses the other request I had when reviewing an earlier version of Mp11. While HOMF were never essential, as the article pointed out, users appreciate more ways to one-line things without having to write a helper type. Some additional primitives are desired, as mentioned later in this review (e.g. min and max functionality) but overall the toolkit is already vast and useful. [What is your evaluation of the implementation? Excellent. The focus on performance is definitely appreciated while we still have to depend on libraries for many of these meta-programming primitives. Ideally many of these would be provided in the standard library and have implementations that only a compiler vendor could provide with built in support, and offer performance beyond what a library could offer. In the meanwhile, the performance offered by Mp11 is great, more than sufficient for my needs, and in my opinion also for the majority of users. In comparison, the tiny C++11 meta-programming library that I have implemented, uses only the obvious C++11 implementations for most functionality, and does not offer the same fast compile times as the equivalents in Mp11. The techniques used by Mp11 via C++11 constexpr, C++14 constexpr, and even C++17 fold expressions, besides improving Mp11 performance, were a valuable source to learn from. Suggestion: Can all the workarounds for MSVC versions 1800 and older for the empty list cases be avoided by instead using a helper trait? i.e. template<template<class...> class L, class... T, template<class...> class P> struct mp_find_if_impl<L<T...>, P> { using type = typename mp_find_if_impl_2<P, T...>::type; }; i.e. Introduce mp_find_if_impl_2 which would then have the obvious implementation as before, only without requiring the MSVC workaround? This is only worth considering if you find it to offer some benefit such as: Additional maintainability of the Mp11 code, with less workarounds, and no costs, e.g. no increase in compilation times as a consequence. [What is your evaluation of the documentation? Very good. The reference documentation is clear, and easily understood. More example and tutorial content before the reference section would always be welcome, but not necessary. Suggestion: The two-part article that Peter wrote (which is referenced in the documentation) is in my opinion so valuable for users to gain better understanding and appreciation of the library that it should be included in the library distribution as part of the documentation. Ideally in the same Asciidoc form as the current documentation, as a supplemental document (or Appendix entry). Suggestion: Does it make sense for the documentation to have a section describing the conventions the library uses, for potential contributors as much as users? e.g. If someone was designing an mp_min_element, should it yield the element type result, or the list index size constant result? Is there an established convention of when an error is acceptable for an empty list versus returning an index? Correction: Under heading mp_find_if<L, P>: "mp_find_f<L, P> is an" should be "mp_find_if<L, P> is an". [What is your evaluation of the potential usefulness of the library? Incredibly useful in its current form, and this is only going to increase as the library is extended based on user requests for additional functionality. Almost every meta-programming primitive that I have needed recently either already exists in Mp11, or I am able to implement using Mp11 with a little effort. During this review I replaced the use of my own meta-programming library in a project of mine without any issues. As part of this review I also tried several exercises where I implemented certain traits and meta-functions using Mp11. Of all the exercises that I attempted, the only one where the library lacked the necessary utility was an "mp_min_element" function: This was an implementation of the typical "type_with_alignment" trait, which can easily be implemented using a "min_element" functionality. Mp11 does not have mp_min, mp_max, mp_min_element, mp_max_element presently, and I believe they should be added because they are useful and users will probably find themselves implementing it. Sure, mp_sort exists, but I would not use a sort when a min_element can suffice. In this case, type_with_alignment<N> could use mp_min_element with a predicate that finds the type in an mp_list of several scalar types, that matches has an alignment of at least N and has the smallest size, and then check that the result element type of the mp_min_element is at least N. The litmus test for me for a meta-programming library is the question: Would I use Mp11 in library code? The answer for me is "yes". If it was part of Boost, I would use it in other Boost libraries (that already require C++11 or higher). [Did you try to use the library? With which compiler(s)? Did you have any problems?] Yes. I used the library as a replacement for an existing meta-programming library of mine in real (non-toy, non-exercise) project code that is compiled with g++ 4.8.5 in c++11 mode for x86 and x86_64 Linux, using Boost 1.64.0, on 64-bit RHEL 6 and measured compilation times. I also used the library in a few exercises that I compiled with g++ 7.1 and clang 4.0.0, for x86 and x86_64 Linux, using the current Boost master branch, for c++11 and c++14, on 64-bit Fedora 26, and again measured compilation times. I also compiled and ran the Mp11 unit tests with the compilers, C++ standard modes, architectures, Boost distributions, and operating systems mentioned. [How much effort did you put into your evaluation? A glance? A quick reading? In-depth study?] More than ten hours over this weekend reading the documentation, reviewing the implementation and tests, using Mp11 in a project replacing my own C++11 meta-programming library, using it in various exercises, and running the Mp11 unit tests with the various compilers, C++ standard modes, targets, and Boost distributions listed above. Prior to the preparation for the review, I had spent some time with an earlier version of Mp11 and comparing it to Metal for implementing a few meta-functions, including the "instantiates_" example from my library: instantiates_<T, templates_<std::set, std::multiset, std::unordered_set> > Where instantiates_ should be implemented in terms of "is_instantiation_of_": is_instantiation_of_<T, std::set> Which has the obvious behavior indicated by the trait name. The Mp11 approach provided by Peter for this case, and the relative ease with which I was able to implement the other meta-functions using Mp11 were a convincing demonstration of the usefulness of the library. [Are you knowledgeable about the problem domain?] Like many of us, I had written a meta-programming library as C++11 language features have become available. Before that, if Boost.MPL solved a problem, more often than not it was convenient and useful enough to just use it, even if writing my own implementation would result in faster compilation times. Peter's article, however, opened my eyes to a more elegant design, and changed how I implemented my C++11 meta-programming library, and in general shaped what I think about meta-programming in modern C++. Thank you Peter for your work on Mp11, for submitting it for inclusion in Boost, and for the articles that motivated it and taught the rest of us. Glen

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[BB++] Now fixes all of your memory leak nightmares
by Phil Bouchard 24 Jul '17

24 Jul '17

Greetings, Now I have an example showing off the cyclic reference handling. Please see: https://github.com/philippeb8/root_ptr/blob/bb++/bbpp2cpp/tests/input2.bb This program correctly outputs: Document::Document(const boost::node_proxy&) auto __0(boost::node_proxy&, int) 1 Document::Document(const boost::node_proxy&) Document::~Document() 2 Document::~Document() So I just came to realize we could use this tool to parse entire projects to generate the right C++ code, after having disabled the 'operator delete', and then run the executable, which still is 3.5x faster than Node.JS. For the newcomer please see: https://github.com/philippeb8/root_ptr/tree/bb++/bbpp2cpp I am going to present this to NASA and company. Meanwhile anybody is welcome to help me out extending the parser to support template syntaxes. Regards, -Phil http://bbplusplus.com/

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[asio] windows service async server crashes after running for a while; though it works fine from console
by Kyoryu Kurayami 24 Jul '17

24 Jul '17

I have an existing console async server that I converted to a windows service. After running for a while (about 1-2 hours), the service would eventually crash caused by stack overflow on different parts of the code (been trying different approach on the code that causes the stack overflow exception but to no avail as it would still crash on a different location) Now, I have been wondering if an async server approach is really suitable for a windows server or should I then opt to convert it to synchronous instead. I used the combination of *io_service::reset()* and* io_service::run() *to block the current code as I've read somewhere that thread running the *io_service::run()* shouldn't immediately exit if it is running as a windows service. Do note that my previous implementation was just calling the *io_service::run() *on another thread, but this doesn't seem to work as per the explanation and solution mentioned above.

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[review][mp11] Review of Mp11
by Glen Fernandes 23 Jul '17

23 Jul '17

What follows is my review of the Mp11 library: [Should the library be accepted into Boost?] Yes. I vote for an unconditional ACCEPT. [What is your evaluation of the design?] Excellent. The design where any template can serve as a list, and any template can serve as a meta-function is both elegant and powerful. The additional quoted meta-function support with utilities such as mp_bind, mp_bind_front, and mp_bind_back, addresses the other request I had when reviewing an earlier version of Mp11. While HOMF were never essential, as the article pointed out, users appreciate more ways to one-line things without having to write a helper type. Some additional primitives are desired, as mentioned later in this review (e.g. min and max functionality) but overall the toolkit is already vast and useful. [What is your evaluation of the implementation? Excellent. The focus on performance is definitely appreciated while we still have to depend on libraries for many of these meta-programming primitives. Ideally many of these would be provided in the standard library and have implementations that only a compiler vendor could provide with built in support, and offer performance beyond what a library could offer. In the meanwhile, the performance offered by Mp11 is great, more than sufficient for my needs, and in my opinion also for the majority of users. In comparison, the tiny C++11 meta-programming library that I have implemented, uses only the obvious C++11 implementations for most functionality, and does not offer the same fast compile times as the equivalents in Mp11. The techniques used by Mp11 via C++11 constexpr, C++14 constexpr, and even C++17 fold expressions, besides improving Mp11 performance, were a valuable source to learn from. Suggestion: Can all the workarounds for MSVC versions 1800 and older for the empty list cases be avoided by instead using a helper trait? i.e. template<template<class...> class L, class... T, template<class...> class P> struct mp_find_if_impl<L<T...>, P> { using type = typename mp_find_if_impl_2<P, T...>::type; }; i.e. Introduce mp_find_if_impl_2 which would then have the obvious implementation as before, only without requiring the MSVC workaround? This is only worth considering if you find it to offer some benefit such as: Additional maintainability of the Mp11 code, with less workarounds, and no costs, e.g. no increase in compilation times as a consequence. [What is your evaluation of the documentation? Very good. The reference documentation is clear, and easily understood. More example and tutorial content before the reference section would always be welcome, but not necessary. Suggestion: The two-part article that Peter wrote (which is referenced in the documentation) is in my opinion so valuable for users to gain better understanding and appreciation of the library that it should be included in the library distribution as part of the documentation. Ideally in the same Asciidoc form as the current documentation, as a supplemental document (or Appendix entry). Suggestion: Does it make sense for the documentation to have a section describing the conventions the library uses, for potential contributors as much as users? e.g. If someone was designing an mp_min_element, should it yield the element type result, or the list index size constant result? Is there an established convention of when an error is acceptable for an empty list versus returning an index? Correction: Under heading mp_find_if<L, P>: "mp_find_f<L, P> is an" should be "mp_find_if<L, P> is an". [What is your evaluation of the potential usefulness of the library? Incredibly useful in its current form, and this is only going to increase as the library is extended based on user requests for additional functionality. Almost every meta-programming primitive that I have needed recently either already exists in Mp11, or I am able to implement using Mp11 with a little effort. During this review I replaced the use of my own meta-programming library in a project of mine without any issues. As part of this review I also tried several exercises where I implemented certain traits and meta-functions using Mp11. Of all the exercises that I attempted, the only one where the library lacked the necessary utility was an "mp_min_element" function: This was an implementation of the typical "type_with_alignment" trait, which can easily be implemented using a "min_element" functionality. Mp11 does not have mp_min, mp_max, mp_min_element, mp_max_element presently, and I believe they should be added because they are useful and users will probably find themselves implementing it. Sure, mp_sort exists, but I would not use a sort when a min_element can suffice. In this case, type_with_alignment<N> could use mp_min_element with a predicate that finds the type in an mp_list of several scalar types, that matches has an alignment of at least N and has the smallest size, and then check that the result element type of the mp_min_element is at least N. The litmus test for me for a meta-programming library is the question: Would I use Mp11 in library code? The answer for me is "yes". If it was part of Boost, I would use it in other Boost libraries (that already require C++11 or higher). [Did you try to use the library? With which compiler(s)? Did you have any problems?] Yes. I used the library as a replacement for an existing meta-programming library of mine in real (non-toy, non-exercise) project code that is compiled with g++ 4.8.5 in c++11 mode for x86 and x86_64 Linux, using Boost 1.64.0, on 64-bit RHEL 6 and measured compilation times. I also used the library in a few exercises that I compiled with g++ 7.1 and clang 4.0.0, for x86 and x86_64 Linux, using the current Boost master branch, for c++11 and c++14, on 64-bit Fedora 26, and again measured compilation times. I also compiled and ran the Mp11 unit tests with the compilers, C++ standard modes, architectures, Boost distributions, and operating systems mentioned. [How much effort did you put into your evaluation? A glance? A quick reading? In-depth study?] More than ten hours over this weekend reading the documentation, reviewing the implementation and tests, using Mp11 in a project replacing my own C++11 meta-programming library, using it in various exercises, and running the Mp11 unit tests with the various compilers, C++ standard modes, targets, and Boost distributions listed above. Prior to the preparation for the review, I had spent some time with an earlier version of Mp11 and comparing it to Metal for implementing a few meta-functions, including the "instantiates_" example from my library: instantiates_<T, templates_<std::set, std::multiset, std::unordered_set> > Where instantiates_ should be implemented in terms of "is_instantiation_of_": is_instantiation_of_<T, std::set> Which has the obvious behavior indicated by the trait name. The Mp11 approach provided by Peter for this case, and the relative ease with which I was able to implement the other meta-functions using Mp11 were a convincing demonstration of the usefulness of the library. [Are you knowledgeable about the problem domain?] Like many of us, I had written a meta-programming library as C++11 language features have become available. Before that, if Boost.MPL solved a problem, more often than not it was convenient and useful enough to just use it, even if writing my own implementation would result in faster compilation times. Peter's article, however, opened my eyes to a more elegant design, and changed how I implemented my C++11 meta-programming library, and in general shaped what I think about meta-programming in modern C++. Thank you Peter for your work on Mp11, for submitting it for inclusion in Boost, and for the articles that motivated it and taught the rest of us. Glen

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[reflection] Which if any reflection library to use
by RAM 22 Jul '17

22 Jul '17

I'm working on code that will need to use reflection, and would like to know if boost already has a reflection library, or uses one preferred library? I know there are future C++ proposals such as those listed below, and am curious if any of them have already been implemented somewhere? http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0590r0.pdf http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0385r2.pdf http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0194r2.html

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Re: [boost] CMake Announcement from Boost Steering Committee
by Brian Wood 22 Jul '17

22 Jul '17

Klemens Morgenstern writes: >Am 21.07.2017 um 22:50 schrieb Niall Douglas via Boost: > >> Some would say that what has been achieved so far is a pale shadow of >> what would have been achieved without the self-serving elitism. If you >> look at the bits of Boost which got into the C++ standard, they are very >> obviously the simple bits. There's a lesson in that. > Let's see: > > Without templates > - boost.system_error > - boost.error_code > - boost.thread > - boost.filesystem > > With type erasure: > - boost.any > - boost.function > > With templates: > - boost.SmartPtr > - boost.variant > - boost.optional > - boost.bind > - boost.tuple > > Template black magic: > - boost.type_traits > - boost.asio (probably as the networking TS) > - boost.EnableIf > > May I ask what you based your statement on? Did you even look at the > list or would actually checking facts be elitism? I think you have to "chew the meat and spit the bones" (*) when it comes to Boost and the standard. And you left out the best one imo -- array. String_view is a good one also. On the other hand, I avoid std::any and I'm skeptical about filesystem. I make conservative use of unique_ptr and try to avoid shared_ptr. (*) My rabbi in Austin, Texas used to say this -- not in relation to Boost though. Brian Ebenezer Enterprises http://webEbenezer.net

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