March 2011 - Boost - lists.boost.org

[chrono] Interoperability with ICL and common concepts
by Joachim Faulhaber 06 Apr '11

06 Apr '11

Hi Vicente and Boost Chronoists, thank you for implementing Boost.Chrono! It's a very fine piece of software :) Currently I'm checking out the usage of chrono types with icl::intervals and interval containers. Obviously, using intervals of chrono::time_points or chrono::durations can be an important use case. Also ICL already works well with other date and time data types from boost data_time, so chrono's interoperability should be at least as easy. A problem here is, that Icl, while working instantly with built in data types (e.g. int, short, double or even int*), for other numeric types (e.g. boost::rational) or types "based on integral types" (e.g. data_time::ptime) I needed to provide adapter code. I think it'd be ideal, if boost libraries interoperated with each other just out of the box, of course. To achive this, we have to find a common understanding of those concepts, that make a seamless interoperability work. I think, this is important work to be done, because it widens the view from one's own library perspective to a broader horizon of generic interplay. The problem: There is a minimal set of requirements that Icl expects for the domain types of intervals and interval containers (1) A zero element, more precisely an identity element w.r.t. the type's composition operation, which usually is +. An assumption that works well for all built in types and many STL-types is, that we get this element by the default constructor T(). (2) A strict weak ordering < (3) For all discrete types and for continuous numeric types: Operators ++, -- (Only pre-variants needed e.g. ++x) (3.1) For discrete types ++/-- increments/decrements by a *least step* (3.2) For continuous numeric types ++/-- increments/decrements by a *unit step*. Most of the functionality of Icl works if requirements (1) through (3) are met. In addition, there are some functions that require a distance type, but only for more specific types, namely for numeric types that use varying interpretations of the origin (zero), like epoch based date and time and pointer-addresses. BTW, do we already have a name for this type of concept? origin_based_equidistant_scalar origin_based_equidifferential_scalar because they are based to an arbitrary origin, but have comparable differences or distances. Or shorter equidistant_scalar equidifferential_scalar because if we emphasize, that by "comparable differences or distances", it is implied that the origin is choosable. May favorite is "equidistant_scalar". This concept reminds me of "Levels of measurement" http://en.wikipedia.org/wiki/Level_of_measurement (4) For such equidistant scalar types D the ICL assumes, that the type of the difference values of D is D::difference_type. To summarize, for a domain type Dom, Icl expects Dom(), <, ++, -- and if dom is a equidistant scalar type we expect an associated type Dom::difference_type to be defined. Now boost::chrono::duration (D1*) Has a default ctor that leaves the type undefined. (D2) Has <, Ok. (D3) Has ++, --, Ok. boost::chrono::time_point (T1) Has a default ctor that implements the semantics assumed by the ICL, Ok. (T2) Has <, Ok. (T3*) Does not have ++, --. (T4*) Does not have difference_type So I end up with 3 of my requirements not met (D1, T3, T4) D1: Default ctor for chrono::duration leaves objects undefined. I assume this is due to efficiency considerations, nevertheless unfavorable from the view point of my library. For all built in types and most of the STL there has been something like an intuitive maybe unconscious may be conscious agreement to assign the identity element w.r.t. the fundamental composing operation of the constructed object's type as the semantics of the default ctor. From an algebraic, generic and interoprability point of view (and IMHO) this is the best choice. This choice has not been taken for chrono::durations, which is a little inconsistent also, because interestingly for its chrono::time_point type the semantic is just the desired one. The possibility of default ctor customization is no remedy, because ICL should ideally be completely "chrono agnostic" and still interoperable. For the same reason duration::zero() is not an option. T3: chrono::time_point does not implement ++ and --. I assume this is because of the specific maths that is designed for chrono::time_points (P) and durations (D) where - : P x P -> D + : P x D -> P + : D x P -> P but + : P x P -> P //verboten But this should not be an argument against ++ and -- because the "least steppable unit" for integral rep types as well as the "unit" for floating point rep types, that is processed by ++ and -- is the same for time_points and durations. T4: Finally, difference_type as the associated type for time_point is not defined. IMO, it should be, because from a concept point of view, chrono::time_point falls in the same equidistant scalar concept that other types are in (e.g. T*, random_access_iterator<T>) and those associate a difference_type. These are the main problems of Icl/Chrono interoperability. There are a few minor ones as well. Let's discuss these first. I hope we can arrive at a solution, where Icl can be chrono agnostic and vica versa and still everything works well together. Based on that, we could fix similar issues for other libs like data_time. Cheers, Joachim -- Interval Container Library [Boost.Icl] http://www.joachim-faulhaber.de

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Why Boost.Build?
by Gregory Crosswhite 06 Apr '11

06 Apr '11

Hey everyone, Is there a reason why Boost uses Boost.Jam/Boost.Build for reasons other than tradition? Does it have advantages over other build systems, in particular CMake (which I consider to be its main competitor)? Are there many people/projects who use Boost.Jam/Boost.Build outside of Boost? These questions are asked purely out of curiosity due to my ignorance of Boost.Jam/Boost.Build, not because I have an axe to grind. Cheers, Greg

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Re: [boost] GSoC Proposal Preparation For Encoding Awared String
by Artyom 05 Apr '11

05 Apr '11

> From: Soares Chen <crf(a)hypershell.org> > > Hi all, > > [snip] > > I think there are several options that I can choose for my project: > 1. To use Chad Nelson's code as base, try to incorporate other ideas > proposed in the mailing list, integrate with Boost.Locale, and make it > Boost quality to submit for review. If this option is chosen, I wish > that Chad Nelson can be my mentor. > 2. To start a new code base, gather and compile ideas suggested in > mailing list, final design decisions made by me and my mentor but not > the community (to keep the project going on fast), make it Boost > quality and submit for review. > 3. To start the boost::string project, where another better string is > reinvented and fix all the weaknesses of std::string. > 4. Adopt different proposal, and improve on existing project such as > Boost.Unicode [2] or Boost.Locale [3] such that it really solves the > encoding awareness problem. > 5. Any other suggestion? Hello, I want you to address several points: It would be very hard to get the consensus about the way to solve the problem. Probably the best and the most wishful thinking solution is to assume that all strings are UTF-8 based, however it is not the reality. The problem is actually not the string but rather the way you code. Even if you create a perfect UTF-8 string and then call fopen(your_perfect_string.c_str(),"r") Under windows... And it would not work <sigh... damn Windows> As you can see from multiple discussions, there are many contradicting requirements about how should string look like and what should it bring with. If you want to provide better Unicode awareness to Boost you don't need new cool utf-XYZ string, you need a policy. I think boost::filesystem v3 is a big step forward, it allows you to use UTF-8 strings on Windows which I think is a really good beginning. This is my opinion. Boost.Locale and several other my projects (CppCMS, CppDB) live happily with std::string. The problem is that in vast majority of cases you don't need encoding aware string, as so many operations you usually do on strings are encoding agnostic. But this is other story. Bottom line, if you want to improve Unicode awareness of Boost I think you need to adopt Boost.Filesystem v3 like policy all over the code base of Boost. 1. Use Wide API as native one in Boost everywhere under Windows 2. Use char * API as native one in Boost everywhere under non-Windows platforms 3. Use std::codecvt to handle this (after many tricks... ) The Unicode String/Encoding Aware String is the last thing to do not the first thing. Why? 1. Because you will never get the consensus about what is the "right-thing" to do (wide, narrow, utf-8, utf-16) etc. Project that are handled and directed by a single source or management like Qt, GTK(mm), Java, C#, Python or others may decide what is the right thing. This will never happen in Boost as it is too pluralistic even in cases where it does not always make sense, just because the way libraries are developed, reviewed and got in - based on public reviews that eventually encourages diversity. 2. Because you would not likely to be able to enforce users to actually use your string. As boost is more about collaboration then enforcement of specific style. 3. Even heavy discussions there hadn't got to any conclusion. So what would happen and final review of your library? My $0.02 Artyom

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[release][1.47] Release branch open + schedule
by Daniel James 05 Apr '11

05 Apr '11

Hello everyone, It's been over a week since the release, so it's time to open the release branch. Since we're running late, and we haven't discussed the changes to the schedule, and I think it helps people to pace their development, we should probably decide on a schedule for this release pretty quickly, and then discuss the schedule for future releases later. We discussed having longer betas, 4 weeks was suggested. If we do that this time, it'll leave a very small window for merging to release, so I think 3 weeks might be better. Something like: 4th April: Release branch closed for beta (bug fixes only). 11th April: Beta target date. 2nd May: Release target date. Note: That's just a proposal, not the actual schedule. It isn't up to me. That's still a tight schedule, maybe a shorter beta or a delayed release would be better. Any thoughts? Daniel

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[lexical cast] Performance improvements
by Antony Polukhin 05 Apr '11

05 Apr '11

Working with Boost Lexical Cast library found that some casts are working really slow. For example, cast from short to int is done via cast from short to char[], and cast from char[] to int. Cast from char* to string is done via string() constructor call and string`s append function call (instead of string constructor call with char array as a parameter). So I wrote patch to Boost Lexical Cast library, that returns Target directly constructed from Source in cases, when: 1) Source and Target are arithmetics (and not char or wchar_t), and all values of Source are in range of Target 2) Source and Target are both char or both wchar_t 3) Source is array of CharT and Target is std::basic_string<CharT, ...> 4) Source and Target are std::basic_string with same template parameters It gives performance boost more than 10 times in case 1) , about 7 times in case 2), and about 1.5 times in cases 3) and 4). Existing tests for Boost Lexical Cast library cover considered cases. Patch was successfully tested on Intel 11.1.072, g++-4.4.5, VC++9 compilers. P.S.: I`m a newbie here, so where shall I send this patch? Shall I test it on other compilers?

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Re: [boost] [lexical-cast] version of lexical_cast in 1.46.1 is quite older than in trunk
by Antony Polukhin 04 Apr '11

04 Apr '11

> "SergV"<serge-voropaev(a)yandex.ru> wrote in message > news:loom.20110329T052451-354@post.gmane.org... > We discovered lexical_cast from 1.43 and 1.46.1 versions do not work in > our > program. But version of lexical_cast from trunk work very well. Version > information: > 1.46.1 - rev. 56161 13.09.2009 > trunk - rev.65279 5.09.2010 > > 1) Is there any reason that release does not include last version > lexical_cast > from trunk? > 2) May be there are a lot of such forgotten files in trunk? There is also some mess with tickets for lexical_cast : some tickets are in bug database for months (and even years). > On Wed, 2011-03-30 at 18:16 +0300, Matthew Chambers wrote: >> Does that mean lexical_cast is orphaned? I'd like to see lexical_cast have optimized conversions for >> string->number and number->string (template specializations using strtol/strtod; or optionally using >> the spirit-based construe_cast). Being able to pass ios flags to control the format (i.e. boolalpha) >> would be nice too [...] >> Which reminds me - lexical_cast error messages are not very >> informative[...] > >Agreed. This should be added as well[...] > >-Matt I can take care about some of this issues, but if lexical_cast is orphaned and not maintained any more it`ll be just wasting time. - Antony

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Data / String Ref library
by Olaf van der Spek 02 Apr '11

02 Apr '11

Hi, A lot of functions take a const void*, size_t pair as two parameters. This is then cast to a const unsigned char* for further processing. Two parameters means you can't easily pass the result of an expression or function call. One parameter would be handier. const std::string& is also used frequently. However, this forces the caller to use (or construct) std::string, which is undesirable and unnecessary. A solution seems simple: data_ref and string_ref, which represent a pointer pair (void/unsigned char and char respectively). string_ref can replace const std::string&, data_ref can replace const void*, size_t. I think this would be a nice addition to Boost. Is there any interest in a library that solves this problem? -- Olaf

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[gsoc] Interest in BGL v2?
by Michael Lopez 01 Apr '11

01 Apr '11

Hello all, My name is Michael and, if there is enough interest from the mailing list, I will be submitting an application for GSoC 2011 to work on the BGL v2. I have been working on a project called Origin ( http://code.google.com/p/origin/) when time permits, that houses the code that I intend to integrate into boost. The project was started by Andrew Sutton and I have taken an active role in its creation. The new library focuses on ease of use, replacement of property maps for labels, data structures with more concise and clear semantics, a new graph concept hierarchy, implementing graph algorithms to align with STL abstractions, and, finally, integrate C++0x into the BGL. I have already worked on the existing BGL back in 2009 for GSoC. While working on the BGL, I started seeing opportunities to bring the BGL more in-line with modern techniques and practices. I found that the library, though robust and quite mature, was lacking in some areas. The most unavoidable being C++0x support. The other design concern was that some of the data structures felt more like meta-programs. This is no good since a meta-program generates types that may model one of many concepts. Another feature that has been on BGL's want list is the implementation of algorithm objects. Some of the algorithm objects are already present in Origin. I realize that this is not a 3 month project. I fully understand that. However, I plan to continue maintaining this library in Origin, as I have been, until it is mature enough for a release and integration into other libraries. Hopefully there is enough interest to get this off of the ground. Please respond with your interests, questions and/or doubts. Michael Lopez

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[lexical-cast] version of lexical_cast in 1.46.1 is quite older than in trunk
by SergV 01 Apr '11

01 Apr '11

We discovered lexical_cast from 1.43 and 1.46.1 versions do not work in our program. But version of lexical_cast from trunk work very well. Version information: 1.46.1 - rev. 56161 13.09.2009 trunk - rev.65279 5.09.2010 1) Is there any reason that release does not include last version lexical_cast from trunk? 2) May be there are a lot of such forgotten files in trunk? Sergey Voropaev

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Re: [boost] [submission] STL-compliant containers with copy-on-write
by Alexandr Sterligov 01 Apr '11

01 Apr '11

I'm working with embedded software and we have to use COW containers pretty often. I haven't found any COW container implementation which may replace STL containers and had to implemented it. It is not possible to make STL containers with COW keeping all semantics of the STL containers. For example, almost any member-function may throw, because copy ctor may throw. It is not always safe to replace std::vector with mine cow_vector, but in most cases it is safe. For example, it is not safe if you have saved constant pointer or constant reference from constant cow_vector. But with std::vector saving addresses is not a good idea as well, because resize, push_back and others may cause address change. In my implementation iterators are safe, for example: cow_vector<int> a; a.push_back( 1 ); cow_vector<int> b; b.push_back( 2 ); cow_vector<int>::const_iterator itA = a.begin(); assert( *itA == 1 ); cow_vector<int>::const_iterator itB = b.begin(); assert( *itB == 2 ); b = a; assert( itA == a.begin() ); assert( itB == b.begin() ); assert( *itA == 1 ); assert( *itB == 1 ); a[0] = 3; // or *a.begin() = 3 assert( itA == a.begin() ); assert( itB == b.begin() ); assert( *itA == 3 ); assert( *itB == 1 ); You example: int* p = &v[1]; // copying is done here v[0] = 1; assert( p == &v[1] ); // still valid as copying was done before. But in following case it won't work now: void test( const cow_vector<int>& a ) { const int *a = &v[1]; v[0] = 1; assert( p != &v[1] ); // sorry, another pointer if internal buffer was shared. } Please note, that it's possible to do copying if any reference or pointer is taken from iterator or container itself, but my current implementation doesn't do it. That's easy to change. > IMO it isn't possible to really make that work anyway since STL > containers expose references to their elements *and* make guarantees > about iterator stability and element layout. For example, if v is a > vector and I do > > v[0] = 1; > > it's not allowed to change the address of v[1] > -- > Dave Abrahams > BoostPro Computing > http://www.boostpro.com ---- Best regards, Alexander Sterligov

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