May 2009 - Boost - lists.preview.boost.org

[futures] is there an updated version of futures
by Yigong Liu 16 May '09

16 May '09

Hello, Is there an updated version of futures lib by Anthony after the review? Is the one dated 20090530 still the latest one publicly avaialble? Thanks Yigong

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[exception] Virtual inheritance with no default constructors
by Adam Badura 16 May '09

16 May '09

The Boost.Exception library mandates that exceptions classes hierarchy should use virtual inheritance (http://www.boost.org/doc/libs/1_39_0/libs/exception/doc/using_virtual_inher…) The document notes that this does not go well with exceptions without default constructors ("(...) Note that virtual bases are initialized directly by the constructor of the most-derived-type (...)") however this should not be a concern as boost::exception provides other means to transport data. What is missing is however documentation that in normal circumstances boost::throw_exception cannot be used with exceptions types which have in their inheritance graph virtual base classes which are not default constructible. This is because boost::enable_current_exception constructs the clone_impl object which inherits the actual exception type and copy-constructs it. However this code will not compile if some base class of the callers exception type is virtual and non-default constructible. In my opinion few changes seem appropriate: 1) Note in the documentation explicitly this requirement (possibility of default construction). 2) Name an entity which should be made friend of exception class to use its non-public default constructor. This entity would be latter used by clone_impl. This way an exception could be default constructible only for this particular use case. 3) Provide means to late-initialize exception object. This would bypass the default construction problem (and goes well with private default constructor as described in 2)). 4) Allow to specify in boost::throw_exception (or similar places) not only the exception type but as well its (virtual) base types so that latter clone_impl could mention them on the initializers list as well and copy-construct them. (As far as I know there is no way of automatic detection of base types thus caller must specify them explicitly - however if I am mistaken such automation would be even better.) Adam Badura

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Re: [boost] [rfc] Unicode GSoC project
by Graham 16 May '09

16 May '09

>What kind of real-world use do people have for random access, anyways? >Even UTF-32 isn't random access for the things I can think of that >people would care about, what with combining codepoints and ligatures >and other such things. I wrote a couple of Unicode text editors that would have been a nightmare if they had not been operating on UTF-32. >As an aside, I'd like to see comparisons between compressed UTF-8 and >compressed UTF-16, since neither one is random-access anyways, and it >seems to me that caring about size of text before compression is about >as important as the performance of a program with the optimizer turned >off. Actually in a few cases I have seen it is not the compressed size but the conversion performance [memory/CPU] that hurts. It is much better to get the correct encoding for the correct use case. Yours, Graham

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Re: [boost] [rfc] Unicode GSoC project
by Graham 15 May '09

15 May '09

>I don't plan on supporting random access for UTF-16. >UTF-16 is still faster than UTF-8 because UTF-8 requires more complex >decoding. >UTF-16 has only two cases, making it easier to optimize branches under >the likely and unlikely case. Dear Mathias, Don't forget surrogates ! Yours, Graham

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Re: [boost] [rfc] Unicode GSoC project
by Graham 15 May '09

15 May '09

>I'll be reviewing it in a while. >I'm not too sure about the memory layout it uses (__uni_char_data could >really be compressed to use less memory for example), nor about the >interface it exposes, but it does seem to work well. >About is_grapheme_break though, isn't the implementation for legacy >grapheme cluster rather than extended ones though? Dear Mathias, The uni car data was laid out in that way for speed and simplicity. Please feel free to do it better. The grapheme break worked off the character attributes and standard rules. If it needs changing or did not cover a later standard, then it should be updated. The principle would not change as it makes the string iterators quite straightforwards.

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[rfc] Unicode GSoC project
by Mathias Gaunard 15 May '09

15 May '09

Hi everyone. I'm in charge of the Unicode Google Summer of Code project. I have been working on range adaptors to iterate over code points in an UTF-x string as well as converting back those code points to UTF-y for the past week and I stopped working on these for a bit to put together some short documentation (which is my first quickbook document, so it may not be very pretty). This is not a documentation of the final work, but rather that of what I'm working on at the moment. I would like to know everyone's opinion of the concepts I am defining, which assume the range that is being worked on is indeed a valid unicode range in a particular encoding, as well as the system used to enforce those concepts. Also, I put the normalization form C as part of the invariant, but maybe that should be something orthogonal. I personally don't think it's really useful for general-purpose text though. While the system doesn't provide conversion from other character sets, this can easily be added by using assume_utf32. For example, using an ISO-8859-1 string as input to assume_utf32 just works, since ISO-8859-1 is included verbatim into Unicode. The documentation contains as well some introductory Unicode material. You can find the documentation online here: http://mathias.gaunard.emi.u-bordeaux1.fr/unicode/doc/html/

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[C++0x] More config macros needed
by Beman Dawes 15 May '09

15 May '09

GCC 4.3 and even more so 4.4 have implemented significant portions of the C++0x core language, and provide lots of C++0x standard library components too. Microsoft 2010 beta 1 will ship "real soon", and it too will have some major C++0x core language features, and also some C++0x standard library components. Thus we need more config macros, particularly those aimed at the standard library. A possible approach: BOOST_NO_CONCEPTS // needed to tell if headers have been conceptized BOOST_NO_*_HDR // for each new C++0x header; * is name of header For example, BOOST_NO_CHRONO_HDR is defined unless header <chrono> is present. I'm proposing we not try to identify whether or no the header is complete. If BOOST_NO_CONCEPTS is defined, the header obviously hasn't been conceptized. Ditto anything else that depends on any other new core language feature that hasn't been implemented. Other incomplete aspects will have to be dealt with by testing the library version. We don't want feature macros to proliferate unduly; they are more work to create and maintain than you might think, and if there are a lot of them it gets very confusing. Comments? --Beman

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[Preprocessor] Can we generate token for #include programmatically ?
by Joel Falcou 15 May '09

15 May '09

Here is what I had in mind #define BASE foo.hpp #include BOOST_PP_STRINGIZE(BOOST_PP_CAT(nt2/support/numeric/functions/scalar/,BASE)) It fails because it seems we can't paste stuff ending with / ... Using fiel iteration, how can I circumvent hsi problem and generate a list of #include whose filename are computed from a sequence of name in a BOOST_PP_SEQ and a given, changing, prefix path ?

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Re: [boost] [rfc] Unicode GSoC project
by Graham 15 May '09

15 May '09

Dear Eric/ Mathias, >That's good, these are needed. Also needed are tables that store the various >character properties, and (hopefully) some parsers that build the tables >directly from the Unicode character database so we can easily rev it >whenever the database changes. A good reloadable character library is in the vault. >And UnicodeGrapheme concept doesn't make sense to me. You say, "A model of >UnicodeGrapheme is a range of Unicode code points that is a single grapheme >cluster in Normalized Form C." A grapheme cluster != Unicode code point. It >may be many code points representing a base character an many zero-width >combining characters. So what exactly is being traversed by a >UnicodeGrapheme range? >It is thus important to be able to apply algorithms with graphemes as the >unit rather than code points to deal with graphemes not representable by a >single code point. I think that a grapheme is more of an iterator concept than a data type concept. By specialising it you will unnecessarily complicate any library. Don't forget that, for example, the current grapheme may start as one character, then suddenly 'grab' the surrounding characters as it makes a combined glyph. I have never found a use case in practise where specialising the grapheme as other than a validated series of code points was helpful. The two cases where graphemes are important is in display [which requires intermediate glyph conversion anyway, and works just as well on runs of code points, so code points are fine] and in editing - and the grapheme-ness here alters during typing. >The Unicode standard also specifies various features such as a collation >algorithm in Technical Standard #10 - Unicode Collation Algorithm for >comparison and ordering of strings with a locale-specific criterion, as >well as mechanisms to iterate over words, sentences and lines Have a look at the character library that I posted in the vault - if you can do graphemes then you can do words, paragraphs etc as they are all just attributes of the characters with simple rules. Graphemes come in to their own for text display and editing and you would need these as well to be able to support that. Don't forget that windows GDI only supports point arithmetic and this means that you need to be able to locate word boundaries to display text well at different scales to work around the GDI scaling rounding [and GDI+ is not much better].

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[1.39.0] Beta candidate
by Beman Dawes 15 May '09

15 May '09

The beta candidate files are up at http://boost.cowic.de/rc/ Before pushing these out to SourceForge, it would be great if a few Boosters could download and try them out as a final QA check. Post your experiences here. Thanks, --Beman

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