February 2015 - Boost - lists.preview.boost.org

Change in range requirements
by Ganssauge, Gottfried 01 Feb '15

01 Feb '15

Please consider the following program: bool predicate(char c) { return c != '0'; } int main (int, char **) { using namespace boost::adaptors; boost::copy( boost::make_iterator_range( std::istream_iterator<char>(std::cin >> std::noskipws), std::istream_iterator<char>()) | filtered(predicate), std::ostream_iterator<char>(std::cout)); return 0; } It works brilliantly with boost-1.54 although std::istream_iterator is only an input iterator. Recently I tried switching to boost-1.57, but suddenly this program stopped working - it won't compile any longer, because istream_iterator is not a forward_iterator: g++ -I ~/source/aurora-python/test-build/parts/boost range_filter.cpp -o range_filter ... # lots of gobbledygook skipped range_filter.cpp:18:64: required from here /home/gotti/source/aurora-python/test-build/parts/boost/boost/concept_check.hpp:210:13: error: conversion from 'boost::iterators::single_pass_traversal_tag' to non-scalar type 'boost::iterators::forward_traversal_tag' requested Y y = x; ^ When I build an equivalent program using boost::filter_iterator it keeps compiling and working fine. Why is it, that the requirements for certain range adaptors (e.g. filtered, transformed) suddenly exclude input ranges? The corresponding iterator adaptors keep working... Gottfried Ganßauge Entwickler Content Engineering & Development ------------------------------------------------------------------ Haufe-Lexware GmbH & Co. KG Ein Unternehmen der Haufe Gruppe Munzinger Str. 9, 79111 Freiburg Tel. +49 761 898-0 Internet: http://www.haufe-lexware.com ------------------------------------------------------------------ Kommanditgesellschaft, Sitz und Registergericht Freiburg, HRA 4408 Komplementäre: Haufe-Lexware Verwaltungs GmbH, Sitz und Registergericht Freiburg, HRB 5557; Martin Laqua Beiratsvorsitzende: Andrea Haufe Geschäftsführung: Isabel Blank, Markus Dränert, Jörg Frey, Birte Hackenjos, Randolf Jessl, Markus Reithwiesner, Joachim Rotzinger, Dr. Carsten Thies ------------------------------------------------------------------

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Regression testing - is procedure changed?
by Dmitry Moskalchuk 01 Feb '15

01 Feb '15

I just found that there was commit into master where whole $BOOST/tools/regression folder was removed - https://github.com/boostorg/boost/commit/50ca965a872e5d454dbdc36c2764e6e3ba…. That means instructions at http://beta.boost.org/development/running_regression_tests.html are not actual anymore. Could any one advice how to do regression testing now? I'm bit confused since I already spent significant time setting up regular regression testing of Boost on Android, and now it become completely broken. -- Dmitry Moskalchuk

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Re: [boost] [Boost-testing] master and develop regressions shunt on "error: Could not find a Jamfile..."
by Jürgen Hunold 01 Feb '15

01 Feb '15

Hi Jim, Am Sonntag, 1. Februar 2015, 05:17:40 schrieb Jim Bell: > Note that I'm using a preinstalled bjam.exe. > > Both master and develop regressions shunt with this in results/bjam.log: Rene has removed tools/regression without removing the reference to it. My PR at https://github.com/boostorg/boost/pull/57 fixes this. I'm not sure if the new regression repository should be re-added as a submodule instead. Yours, Jürgen -- * Dipl.-Math. Jürgen Hunold ! * voice: ++49 4257 300 ! Fährstraße 1 * fax : ++49 4257 300 ! 31609 Balge/Sebbenhausen * jhunold(a)gmx.eu ! Germany

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Automatically updating libs/maintainers.txt
by Daniel James 01 Feb '15

01 Feb '15

Hi, I've just written a little script to update libs/maintainers.txt from the library metadata. You can see the main changes here: https://github.com/boostorg/boost/commit/94897806350320ac87d629bb933d5aea4d… I've only done this on develop so far, so nothing's final. I will do the library list as well soon, but that might be a bit more disruptive. Daniel

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[type_traits] Rewrite and dependency free version
by John Maddock 01 Feb '15

01 Feb '15

I'm going to throw this out there to see what folks think: In a branch called "Version2", see https://github.com/boostorg/type_traits/tree/Version2 is a partially rewritten type_traits lib: it doesn't yet contain all the traits of the old one, but there's a pretty good selection to test. The main pros for this version are: 1) Zero dependencies other than Boost.Config. 2) No horrible macro-obfuscation - all "real code", making it easier to read and maintain. 3) Substantially reduced template instantiations where practical - often half as many as before. 4) Substantially reduced #includes - the aim is that all files should include only what they need and no more - with what's needed determined by the actual implementation variant when appropriate. There were also a lot of spurious #includes left over from old workarounds no longer used. The main cons: 1) I don't know what I've broken, but surely something, you can help by testing but I would guess we would never be 100% sure it's all right until it's out in the field. This is the main reason for avoiding this until now. 2) MPL interoperability should still work, but files which expect type_traits headers to have included mpl ones will be broken unless they explicitly include what they need. 3) Current MPL inter-operability is fragile see https://github.com/boostorg/type_traits/blob/Version2/include/boost/type_tr… 4) Function dispatching to an mpl::bool_ involves an (inline) function call where as the old inheritance scheme did not. This should mostly disappear once optimizations are turned on, but is still a potential issue for some folks I suspect. 5) I haven't got to the "difficult" headers like common_type.hpp yet. 6) Whatever I've forgotten ;) Of course (2), (3) and (4) could be solved by making mpl's bool.hpp some kind of "core" header. So... what I need from you kind folks is: * Is this the right way forward? * Can you test with your favourite compilers and compare with results for develop - So far I've tested with msvc-10,11,12,14 Intel 14,15, GCC-4.5.4...4.9.1, plus a reasonably recent clang. * If anyone would like to help converting further traits all help would be much appreciated.... Oh and the compiler requirements in the docs are all wildly out of date too... Regards, John.

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A possible solution to the SFINAE/decltype puzzler
by pfultz2 01 Feb '15

01 Feb '15

A couple years ago Eric Niebler posted a question on here about improving error messages with SFINAE and trailing decltype: http://boost.2283326.n4.nabble.com/C-11-decltype-SFINAE-puzzler-td4632622.h… The problem was getting a useful error message when writing something like this: struct h_f { template<class T> auto operator()(T x) const -> decltype(*x) { return *x; } }; constexpr static h_f h = {}; struct g_f { template<class T> auto operator()(T x) const -> decltype(h(x)) { return h(x); } }; constexpr static g_f g = {}; struct f_f { template<class T> auto operator()(T x) const -> decltype(g(x)) { return g(x); }; }; constexpr static f_f f = {}; int main() { f(0); } His solution at the time was to turn the substitution failures into errors. Of course, this has some problems as well. First, it removes the template constraints from the functions. Secondly, it can produce more errors(rather than one error with multiple "notes"). Ideally, it would be better to transport to the top the substitution failures. Well, using template aliases this can be done: https://gist.github.com/pfultz2/3d66795ef18361699fbb When I compile this code I get an error like this: reveal1.cpp:104:5: error: no matching function for call to object of type 'const reveal_failure<f_f>' f(0); ^ reveal1.cpp:56:10: note: candidate template ignored: substitution failure [with Ts = <int>, Id = identity]: indirection requires pointer operand ('int' invalid) auto operator()(Ts&&... xs) const -> decltype(F()(std::forward<Ts>(xs)...)) ^ Now, when there is multiple overloads(or multiple notes), this can be extended to handle this situation, as well. An overload for each note, can be added. Plus, the backtrace can be "flattened" so that only the "leafs" are shown. I do this here: https://gist.github.com/pfultz2/ac74129e73393f798e41 So for the 'advance' function it shows an error like this: reveal2.cpp:288:5: error: no matching function for call to object of type 'reveal<conditional<advance_advanceable, advance_decrementable, advance_incrementable> >' advance(f, 1); ^~~~~~~ reveal2.cpp:215:13: note: candidate template ignored: disabled by 'enable_if' [with Ts = <foo &, int>, Id = identity] REQUIRE_OF(models<Advanceable(Iterator, int)>()); ^ reveal2.cpp:7:82: note: expanded from macro 'REQUIRE_OF' #define REQUIRE_OF(...) template<class Id> using apply = typename std::enable_if<(Id()(__VA_ARGS__)), int>::type ^ reveal2.cpp:234:13: note: candidate template ignored: disabled by 'enable_if' [with Ts = <foo &, int>, Id = identity] REQUIRE_OF(models<Decrementable(Iterator)>()); ^ reveal2.cpp:7:82: note: expanded from macro 'REQUIRE_OF' #define REQUIRE_OF(...) template<class Id> using apply = typename std::enable_if<(Id()(__VA_ARGS__)), int>::type ^ reveal2.cpp:258:13: note: candidate template ignored: disabled by 'enable_if' [with Ts = <foo &, int>, Id = identity] REQUIRE_OF(models<Incrementable(Iterator)>()); ^ reveal2.cpp:7:82: note: expanded from macro 'REQUIRE_OF' #define REQUIRE_OF(...) template<class Id> using apply = typename std::enable_if<(Id()(__VA_ARGS__)), int>::type ^ reveal2.cpp:168:10: note: candidate template ignored: substitution failure [with Ts = <foo &, int>]: no matching function for call to object of type 'advance_advanceable' auto operator()(Ts&&... xs) -> decltype(F1()(std::forward<Ts>(xs)...)) ^ ~~ reveal2.cpp:174:10: note: candidate template ignored: substitution failure [with Ts = <foo &, int>, $1 = 0]: no matching function for call to object of type 'conditional<advance_decrementable, advance_incrementable>' auto operator()(Ts&&... xs) -> decltype(F2()(std::forward<Ts>(xs)...)) ^ So there is one note for each overload of `Advanceable`, `Decrementable`, and `Incrementable`. There is two additional notes at the bottom, this comes from the original function(ideally it would need to be normalized). I go into more detail about how this works here: http://pfultz2.com/blog/2015/01/31/improving-error-messages/ However, this is isn't quite perfect yet. First, it requires putting the type requirements into a nested failure struct. Secondly, not all the types are reported back to clang. It doesn't show the user what type `Iterator` is. Ideally, it would be nice if there was a way to push clang to report the substitution failure at least one level deeper for an expression. This is about as close as I've gotten. Is there any feedback? Questions? Perhaps some improvements? Thanks, Paul Fultz II -- View this message in context: http://boost.2283326.n4.nabble.com/A-possible-solution-to-the-SFINAE-declty… Sent from the Boost - Dev mailing list archive at Nabble.com.

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