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[program options] Support for storage to 'optional' objects
by Chris Glover 15 Oct '12

15 Oct '12

Hi, Recently when using the Boost Program options library, I was surprised to find that I was unable to pass a boost.optional object to store supplied options in. For example; namespace bpo = boost::program_options; boost::optional<std::string> opt_str; bpo::options_description desc("Allowed options"); desc.add_options() ("help", "produce help message") ("opt", bpo::value(&opt_str), "Something optional") // Store value of 'opt' in 'opt_str' ; What I expected to happen would be that 'opt_str' would be valid if 'opt' is supplied by the user, and not valid otherwise. However, the above code causes a compile error deep within lexical_cast because, of course, performing such an operation on a boost.optional doesn't make sense. The attached patch to Program Options rectifies the issue by filtering out optional objects within before calling lexical_cast, but to be honest, I'm not sure if this is the correct approach or if this is even a desirable feature. I like the idea of setting an optional object this way instead of testing the variables_map later on, but perhaps there's something I am missing or a better way to accomplish the same thing. Please have a look and let me know your thoughts. Thanks, -- chris

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[contract] concepts: pseudo-signatures vs. usage patterns
by Lorenzo Caminiti 14 Oct '12

14 Oct '12

On Tue, Oct 9, 2012 at 7:16 PM, Dave Abrahams <dave(a)boostpro.com> wrote: > on Tue Oct 09 2012, Lorenzo Caminiti <lorcaminiti-AT-gmail.com> wrote: >> >> I made a first attempt to sketch how N3351-like concepts will look >> into Boost.Contract (just for the find algorithm and its concepts for >> now): >> [...] >> Please tell me what you think now > > Since you asked what I think, > > "pseudo-signatures > usage patterns" Hello all, Can we write down pros and cons for concepts implemented via pseudo-signatures (C++0x-like and Boost.Generic) vs. usage patterns (N3351 and Boost.Contract)? Who wants to start? Matt, Dave, Andrzej, ... I can compile a qbk table with what we discuss. Thanks. --Lorenzo

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[quickbook] Cross-Referencing Source-Snippets
by Matt Calabrese 14 Oct '12

14 Oct '12

I'm currently documenting the Generic library and the documentation itself imports a lot of code from the source files directly (the best documentation for a concept generally involves showing the concept definition itself, and importing it means the code won't be out of sync with the documentation). This imported source code references other concepts and I'd like to be able to have each one of these referenced concepts be a clickable link that brings the person to the documentation for that concept (I.E. in http://generic.nfshost.com/generic/standard_concepts/concepts/equivalencere… the user should be able to click on "Predicate" in the imported source code to see the documentation for the Predicate concept). So, I tried the simplest solution -- make a quickbook macro called Predicate that results in a link to the corresponding Predicate documentation. After a quick test, everything worked fine with one exception -- the name of the section linked to is also "Predicate" and that seems to be causing the link in the generated table of contents to no longer work properly, pointing to a page that doesn't exist even though it displays the link with the proper name (note that the cross-reference links still seem to work fine, it's just the links in the table of contents that break). I realize that I'm doing something hacky here, so if anyone has a better solution, let me know. If this is the best approach, is there a way that I can keep the name of the section the same as the macro name? I.E. Is there some trick I can use to prevent the macro from being expanded when I use it in the section declaration? Keep in mind that I can't simply use templates here instead of macros because the macros are expanded from within imported, working code snippets. I also can't postpone defining the macro until after the section is declared since sections are presented in alphabetical order, meaning that an earlier section's code may reference a later section's code based on dependencies. -- -Matt Calabrese

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[pointee] partially specialize for pointer types?
by Jeffrey Lee Hellrung, Jr. 14 Oct '12

14 Oct '12

Right now, boost::pointee<T*> is evaluated to T via evaluation of boost::detail::is_incrementable<T*>. Unfortunately, this causes a hard error when T is incomplete. See [1] for motivation on why this might be undesirable. It seems there's no loss in partially specializing boost::pointee for pointer types to allow it to be used for incomplete types. Ditto for boost::indirect_reference. Are there issues with this that I might be missing? As both pointee and indirect_reference seem to fall under the purview of Boost.Iterator, I would take responsibility of making this change and adding appropriate unit tests for the incomplete type case. - Jeff [1] https://svn.boost.org/trac/boost/ticket/5965

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Terminology check.
by Larisse Voufo 14 Oct '12

14 Oct '12

Hello -- What would happen to be the C++ word for: name lookup + overload resolution? I would have thought it was "name resolution", but the standard seems to be suggesting otherwise. Thanks, -- Larisse.

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[iterator] [documentation] need help generating
by Jeffrey Lee Hellrung, Jr. 13 Oct '12

13 Oct '12

I'm a n00b regarding Boost's documentation generation. I've gone through https://svn.boost.org/trac/boost/wiki/BoostDocs/GettingStarted to set up my system (Windows 7, MSVC9, try to do everything from the Windows command line). I then navigate to trunk\libs\iterator\doc and run b2 (the b2 I have from the 1.51.0 release; would that matter?). I get -------- don't know how to make <p..\..\..\bin.v2\libs\iterator\doc\msvc-9.0\debug\threading-multi-object(xinclude-scanner)@987>iterator.xml ...found 37 targets... ...updating 5 targets... ...can't find 1 target... ...can't make 2 targets... common.mkdir ..\..\..\bin.v2\libs\iterator\doc common.mkdir ..\..\..\bin.v2\libs\iterator\doc\msvc-9.0 common.mkdir ..\..\..\bin.v2\libs\iterator\doc\msvc-9.0\debug common.mkdir ..\..\..\bin.v2\libs\iterator\doc\msvc-9.0\debug\threading-multi quickbook.quickbook-to-boostbook ..\..\..\bin.v2\libs\iterator\doc\msvc-9.0\debug\threading-multi\iterator.xml Generating Output File: ..\..\..\bin.v2\libs\iterator\doc\msvc-9.0\debug\threading-multi\iterator.xml quickbook\iterator.qbk:24: warning: Quickbook version undefined. Version 1.1 is assumed quickbook\concepts.qbk:159: warning: line breaks generate invalid boostbook (will only note first occurrence). quickbook\facade.qbk:491: warning: in column:6, unexpected character: ` [...lots more warnings of this nature...] quickbook\facade.qbk:612: warning: in column:52, unexpected character: ` quickbook\utilities.qbk:77: warning: in column:14, unexpected character: ` quickbook\utilities.qbk:77: warning: in column:44, unexpected character: ` quickbook\utilities.qbk:79: warning: in column:12, unexpected character: ` quickbook\utilities.qbk:79: warning: in column:15, unexpected character: ` quickbook\utilities.qbk:109: warning: in column:14, unexpected character: ` quickbook\utilities.qbk:109: warning: in column:46, unexpected character: ` ...skipped <p..\..\..\bin.v2\libs\iterator\doc\msvc-9.0\debug\threading-multi>iterator.docbook for lack of <p..\..\..\bin.v2\libs\iterator\doc\msvc-9.0\debug\threading-multi-object(xinclude-scanner)@987>iterator.xml... ...skipped <phtml>standalone_HTML.manifest for lack of <p..\..\..\bin.v2\libs\iterator\doc\msvc-9.0\debug\threading-multi>iterator.docbook... ...skipped 2 targets... ...updated 6 targets... -------- Then I run it again: -------- ...found 37 targets... ...updating 2 targets... xslt-xsltproc.windows ..\..\..\bin.v2\libs\iterator\doc\msvc-9.0\debug\threading -multi\iterator.docbook xslt-xsltproc-dir.windows html\standalone_HTML.manifest Error: no ID for constraint linkend: indirecct. ...updated 2 targets... -------- This seems to throw everything into trunk\libs\iterator\doc\html. However, these generated html documents don't seem to be the same as those in the Boost releases. For example, the table of contents is deeper in the generated index.html than the 1.51.0 release one (which looks be identical to trunk/libs/iterator/doc/index.html), and it lacks documentation for function_input_iterator. It seems like I'm doing something wrong, and I'm not really sure what to make of the various errors and warnings I'm getting. Would anyone be kind of enough to help me out here? Oh, my user-config.jam file, located in "C:/Users/Jeffrey/", looks like -------- using xsltproc : C:/Users/Jeffrey/boost-tools/libxslt-1.1.26.win32/bin/xsltproc.exe ; using boostbook : C:/Users/Jeffrey/boost-tools/xml/docbook-xsl-1.77.1 : C:/Users/Jeffrey/boost-tools/xml/docbook-xml-4.2 ; using quickbook : %BOOST_ROOT%/dist/bin/quickbook ; -------- BOOST_ROOT refers to my Boost 1.51.0 installation, and C:/Users/Jeffrey/boost-tools/bin is part of my path. Let me know if other information is needed. TIA, - Jeff

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[addressof] Intel C++ 13 Warning (Cannot be suppressed)
by Joshua Boyce 13 Oct '12

13 Oct '12

addressof.hpp causes a warning under Intel C++ 13 when using the highest warning level, which cannot be suppressed using the regular #pragma directives. This causes problems when compiling user code with warnings as errors, as the header causes an error which cannot be disabled. The root of the issue seems to be that ICC thinks that an rvalue is being passed to a function which takes a non-const ref, however in this case I think it's a false positive (ICC apparently isn't smart enough to notice and analyze the implicit conversion operator). My simple workaround is to turn the temporary into an lvalue and pass that instead. After making this change I tested under MSVC 12, GCC 4.7, ICC 13, and Clang 3.1 (all under Windows) and recorded no changes in number of failed compiles or tests. Is this an acceptable change that could be merged into trunk? Thanks.

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[contract] toward N3351 concepts
by Lorenzo Caminiti 13 Oct '12

13 Oct '12

Hello all, I'm reading N3351: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3351.pdf It's a bottom-up approach to define concepts starting from what's needed by STL algorithms. So far so good--I like it probably more than C++0x concept proposals--N331 is simpler :) However, N3351 STL design is not fully compatible with the current STL specifications--maybe N3351 is better, more mathematically sound? In N3351, concepts are boolean constants: ``We can define concepts as simple (constant) Boolean expressions. This is useful when building constraints predicated on non-syntactic and non-semantics properties of types.`` So I can implement concepts in C++11 as boolean meta-functions using expression SFINAE to check the requirements and enable_if to disable generic algorithms when the instantiated types don't model the concepts (i.e., the concept's boolean meta-function is false). For example, that's the case for the bool{a== b} and bool{a!=b} expressions of the EqualityComparable concept below. However, N3351 says that axioms should not be checked by the compiler... ``Axioms express the semantics of a concept’s required syntax; they are assumed to be true and must not be checked by the compiler beyond conformance to the C++ syntax. Any additional checking is beyond the scope of the compiler’s translation requirements. The compiler must not generate code that evaluates axioms as preconditions, either. This could lead to program errors if the evaluated assertions have side effects. For example, asserting that distance(first, last) > 1 when the type of those iterators is istream_iterator will consume the first element of the range, causing the assertion to pass, but the algorithm to have undefined behavior.'' So what am I supposed to do with axioms? Do nothing? Axioms are just "comments" that document the semantic? For example: `` concept EqualityComparable<typename T> = requires (T a, T b, T c) { bool { a == b }; bool { a != b }; axiom { a == b <=> eq(a, b); } // true equality axiom { a == a; // reflexive a == b => b == a; // symmetric a == b && b == c => a == c; // transitive } axiom { a != b <=> !(a == b); } // complement }; So, EqualityComparable<T> is true if T 1. has == and != with result types that can be converted to bool 2. == compares for true equality 3. == is reflexive, symmetric, and transitive 4. != is the complement of == However, the compiler can only check the first of these conditions. The rest must be verified through other means (i.e. manually). '' Thanks, --Lorenzo

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Re: [boost] Boost CRC maintainer (Daryle Walker) missing in action?
by Olaf van der Spek 13 Oct '12

13 Oct '12

On Sat, Mar 10, 2012 at 2:06 PM, Olaf van der Spek <ml(a)vdspek.org> wrote: > On Mon, Nov 28, 2011 at 1:11 AM, Daryle Walker <darylew(a)gmail.com> wrote: >> I can look at it once I've finished my new setup. >> >> I had to reset my computer after a partial crash years ago. I never >> got around to recreating my programming setup. My computer had been >> at its maximum Operating System level back then, which is now 3 >> versions behind. For the past few months, I've had my sister's old >> laptop, with Windows Vista, and am trying to add a programming setup >> to it now. > > Hi Daryle, > > Any updates on these two? > > https://svn.boost.org/trac/boost/ticket/3030 > https://svn.boost.org/trac/boost/ticket/5970 Mr Walker? Have you gone missing in action again? :( -- Olaf

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[1.52] compile errors with xcode / apple llvm 4.1
by Jochen Wilhelmy 13 Oct '12

13 Oct '12

Hi! Had anybody success in compiling an own project that uses boost with xcode 4.5.1 / apple llvm 4.1? I get this error: In file included from /Users/jwilhelmy/Coding/Install/include/boost/type_traits.hpp:35: In file included from /Users/jwilhelmy/Coding/Install/include/boost/type_traits/has_operator.hpp:42: In file included from /Users/jwilhelmy/Coding/Install/include/boost/type_traits/has_post_decrement.hpp:34: .../boost/type_traits/detail/has_postfix_operator.hpp:143:109: error: expected expression BOOST_STATIC_CONSTANT(bool, value = (sizeof(check(((make<Lhs>() BOOST_TT_TRAIT_OP),make<has_operator>())))==sizeof(::boost::type_traits::yes_type))); ^ .../boost/config/suffix.hpp:392:72: note: expanded from macro 'BOOST_STATIC_CONSTANT' # define BOOST_STATIC_CONSTANT(type, assignment) static const type assignment ^ -Jochen

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