October 2008 - Boost - lists.boost.org

[shared_ptr] towards a static_cast applied to smart_ptr
by vicente.botet 03 Oct '08

03 Oct '08

Hello Peter, the following simplified example do not compile when DONT_NOT_COMPILE is defined. #include <boost/shared_ptr.hpp> using namespace boost; struct X { int i; }; int main () { shared_ptr<X> ptrX1(new X()); shared_ptr<void> ptr_void(ptrX1); #if DONT_NOT_COMPILE shared_ptr<X> ptrX2(ptr_void); #endif return 0; } test_thread_shared_ptr.cpp: In function `int main()': test_thread_shared_ptr.cpp:37: error: no matching function for call to `boost::s hared_ptr<X>::shared_ptr(boost::shared_ptr<void>&)' ../../../boost/shared_ptr.hpp:154: note: candidates are: boost::shared_ptr<X>::s hared_ptr(const boost::shared_ptr<X>&) ../../../boost/shared_ptr.hpp:241: note: boost::shared_ptr< <template-parameter -1-1> >::shared_ptr(const boost::detail::shared_count&, T*) [with T = X] ../../../boost/shared_ptr.hpp:167: note: boost::shared_ptr< <template-parameter -1-1> >::shared_ptr() [with T = X] This is normal as void* is not convertibel to X*. But in my program I can ensure that the pointeed object by ptr_void is a X pointer. So it would be safe to do a kind of static_cast on shared_ptr. At the end smart pointers should behave like pointers. My real use case is a map of void* to shared_ptr<void>. I insert pairs of T* and shared_ptr<T> and I want be able to static_cast the resulting shared_ptr<void> of find function to shared_ptr<T>. Can I achieve this already? I was thinking is something like something like shared_ptr<X> ptrX2(boost::static_cast<shared_ptr<X> >(ptr_void)); If we can not achieve this now, I think that it should be not too dificult to implement inside your library. Do you think that this is an interesting feature to be included in the Boost.SmartPtr library? Best, Vicente Botet

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sandbox:spatialIndex example compilation fails on gcc-4.2
by Sandeep Gupta 03 Oct '08

03 Oct '08

Hi, Not sure if this known problem but example.cpp of spatial_index library fails to compile out of the box (this is latest version check out from svn repository). A brief look at the code shows that all avatar of spatial_index take two template-arguments but example calls it with one argument. Please find the error message pasted below. Thanks sandeep example.cpp:14: error: wrong number of template arguments (1, should be 3) ../../../boost/spatial_index/spatial_index.hpp:29: error: provided for 'template<class Point, class Value, class Index> class boost::spatial_index::spatial_index' example.cpp:14: error: invalid type in declaration before ';' token example.cpp:17: error: request for member 'get_nothing_count' in 'object', which is of non-class type 'int' example.cpp:18: error: request for member 'nothing' in 'object', which is of non-class type 'int' example.cpp:19: error: request for member 'get_nothing_count' in 'object', which is of non-class type 'int' example.cpp:21: error: request for member 'get_call_count' in 'object', which is of non-class type 'int' example.cpp:22: error: request for member 'nothing' in 'object', which is of non-class type 'int' example.cpp:23: error: request for member 'get_call_count' in 'object', which is of non-class type 'int' example.cpp:24: error: request for member 'get_nothing_count' in 'object', which is of non-class type 'int'

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[Phoenix] review
by Giovanni Piero Deretta 02 Oct '08

02 Oct '08

- Please always state in your review, whether you think the library should be accepted as a Boost library! Having to review a library that is already expected to change is hard, OTOH functional programming in c++ need to go beyond boost.lambda (which has been basically in maintenance mode for a long time), and I think that Phoenix is the way to the future. Thus I think that Phoenix should be accepted. I support having an extra mini review after the implementation has been updated, but my vote is not under this condition. I think that the review plan proposed by Eric is great. - What is your evaluation of the documentation? I think that documentation of Phoenix is probably the most important part of the library and I consider it of high quality: I've been an happy lambda user for a couple of years. I went beyond its documented interface and started to play with its internal. I've been able to add lazy functions to lambda and other nice additions. But I would never even have attempted that if I hadn't been exposed to the Phoenix documentation. I've never really used the phoenix library, but I've read its documentation many times (starting maybe 4 years ago, I think it was the old V1 documentation). I remember that the first time I read it I understood basically nothing. But it got me interested in functional programming. Every time I read it I learned a bit more until something clicked. After that everything seemed so obvious. Thanks Joel, you exposed me to a new world. - What is your evaluation of the design? Very good. I'm a big fan of lazy functions (I try to make all my polymorphic functions object lazy, and leave bind only for good old function pointers), and I hope that Joel will make them 'optionally lazy'. But even if he didn't, thanks to phoenix extensibility, it wouldn't be hard to add it on top of the current design. Again, I vote for always requiring lambda[] around every lambda expression, as this could really help to solve many problems, like assignability and operator& problems. It will also open up the road for further improvements, like overriding capture defaults or selecting perfect forwarding. About perfect forwarding: it would be great if phoenix allowed it by default at least on compilers that support rvalue references. IMHO result_of support is necessary for a library released today :). I cannot really comment on the details of extension interface as it seems that it is bound to change, but I think it is, together with lazy functions, the bigger improvement to boost.lambda. - What is your evaluation of the implementation? I did only take a quick glance at the implementation, but the code looks surprisingly clean (even if comments are a bit spotty), with few compiler workarounds. This is most likely due to the clean separations of the various parts of the library. Even the use of the preprocessor seems limited to the strict neces. I did notice that stl function object instances are declared, as const, in an header file. This could cause ODR violations. - What is your evaluation of the potential usefulness of the library? Great, at least if one is interested in a more functional approach to C++. - Did you try to use the library? With what compiler? Did you have any problems? I tried some examples with gcc 4.2. Didn't have any problem after I figured out that the header placement inside spirit changed from boost 1.35 to 1.36. - How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? An in depth study of the documentation and a quick reading of the source. - Are you knowledgeable about the problem domain? A bit. I've never implemented a full lambda library, but played a lot with boost.lambda. [ I would have liked to make a more in-depth review, but I'm in the middle of a deadline, sorry] -- gpd

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[Review] Phoenix review starts today, September 21st
by Hartmut Kaiser 02 Oct '08

02 Oct '08

Hi all, The review of Joel de Guzmans and Dan Marsdens Phoenix V2 library starts today, September 21st 2008, and will end on September 30th. I really hope to see your vote and your participation in the discussions on the Boost mailing lists! --------------------------------------------------- About the library: The Phoenix library enables FP techniques such as higher order functions, lambda (unnamed functions), currying (partial function application) and lazy evaluation in C++. The focus is more on usefulness and practicality than purity, elegance and strict adherence to FP principles. History: Phoenix is a mature library from years of use as a sub-project under Spirit where it serves its purpose for semantic action handling. Phoenix predates Lambda's acceptance into Boost, but not Lambda itself. When Lambda was reviewed, it was concluded that both libraries were to be merged, and work on it began, culminating in Phoenix V2, what you are seeing now (an interesting offshoot of this effort is Boost.Fusion. We needed a powerful tuple facility with algorithms to get the design right). Recently, Eric Niebler did a (fully compatible) port to proto making use of boost.typeof for result type deduction. Eric's port, while significant, will not be the subject of the review, but can be regarded as the future of Phoenix (Phoenix V3). Phoenix V2 is currently a utility library included with Spirit V2 and therefore is already available from the latest Boost distributions (headers: $BOOST_ROOT/boost/spirit/home/phoenix, docs: $BOOST_ROOT/libs/spirit/phoenix, or http://www.boost.org/doc/libs/1_36_0/libs/spirit/phoenix/index.html) Phoenix V2 is a very important infrastructure library, IHMO. It has been used for several other library writing efforts already, most notably, Spirit V2. --------------------------------------------------- Please always state in your review, whether you think the library should be accepted as a Boost library! Additionally please consider giving feedback on the following general topics: - What is your evaluation of the design? - What is your evaluation of the implementation? - What is your evaluation of the documentation? - What is your evaluation of the potential usefulness of the library? - Did you try to use the library? With what compiler? Did you have any problems? - How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? - Are you knowledgeable about the problem domain? Regards Hartmut Review Manager

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error during compliation of documentation for SpatialIndexes
by Sandeep Gupta 02 Oct '08

02 Oct '08

Hi, I am getting following error while compiling the docs for spacial_indexing: ...patience... ...found 1299 targets... ...updating 2 targets... xslt-xsltproc ../../../bin.v2/libs/spatial_index/doc/gcc-4.2/debug/spatial_index_xml.docbook ../../../bin.v2/libs/spatial_index/doc/gcc-4.2/debug/spatial_index_xml.xml:82: parser error : Opening and ending tag mismatch: section line 44 and library </library> ^ ../../../bin.v2/libs/spatial_index/doc/gcc-4.2/debug/spatial_index_xml.xml:83: parser error : Premature end of data in tag library line 3 ^ unable to parse ../../../bin.v2/libs/spatial_index/doc/gcc-4.2/debug/spatial_index_xml.xml XML_CATALOG_FILES=/home/sandeep/develop/libraries/boost-trunk/bin.v2/boostbook_catalog.xml export XML_CATALOG_FILES "/usr/bin/X11/xsltproc" --stringparam annotation.support "1" --stringparam chunk.first.sections "1" --stringparam chunk.section.depth "3" --stringparam generate.section.toc.level "3" --stringparam toc.max.depth "3" --stringparam toc.section.depth "3" --xinclude -o "../../../bin.v2/libs/spatial_index/doc/gcc-4.2/debug/spatial_index_xml.docbook" "/home/sandeep/develop/libraries/boost-trunk/tools/boostbook/xsl/docbook.xsl" "../../../bin.v2/libs/spatial_index/doc/gcc-4.2/debug/spatial_index_xml.xml" ...failed xslt-xsltproc ../../../bin.v2/libs/spatial_index/doc/gcc-4.2/debug/spatial_index_xml.docbook... ...skipped <phtml>standalone_HTML.manifest for lack of <p../../../bin.v2/libs/spatial_index/doc/gcc-4.2/debug>spatial_index_xml.docbook... ...failed updating 1 target... ...skipped 1 target... Thanks sandeep

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Re: [boost] [switch] Is there any interest in library switch extention?
by Kasra Nassiri(Math & ComSci) 01 Oct '08

01 Oct '08

>I hardly see how this could work for a O(1) lookup (the point of the >switch statement). I have found a compile time solution! However, we need C++0x :( A hash functions with output type of <int> so we could embed the statement in a normal switch statement on C++0x. #define BOOST_SWITCH( object ) switch ( const_hash_function(object) ) #define BOOST_CASE( case_object ) case const_hash_function(case_object) #define BOOST_DEFAULT default So we could write code like: BOOST_SWITCH( "Hello World" ) { BOOST_CASE("wrong value"): BOOST_CASE("another wrong value"): cout << "Reached wrong statements" << endl; BOOST_BREAK; BOOST_DEFAULT: cout << "Hello World" << endl; }; What I like to add is a reference to the value of the BOOST_SWITCH(...), in this example "Hello World".

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[integer] Promotion of endian library code from vault
by Neil Mayhew 01 Oct '08

01 Oct '08

On 2006-07-22 12:21:01, Beman Dawes wrote: > [boost] [integer] endian-0.6 posted w/ names changed > endian-0.6.zip has been posted in the integer directory of the file > vault at http://boost-consulting.com/vault/ This code is still in the vault, but I'd like to see it in the main part of boost. What needs to be done to make this happen? The endian library is exactly what I've been looking for, and I would really like to use it in my work, but I can't justify that to my colleagues if it's not an official part of boost. I would hate to become yet another person that reinvents this particular wheel. However, I notice there was a lot of discussion <http://lists.boost.org/Archives/boost/2006/07/108125.php> about PODs vs constructors, because of unions, so maybe not enough consensus was reached? There were some interesting proposals but no agreed-upon solution. In which case, I suspect that people will need to copy the code and each hack it to suit their own purposes, which is not what boost is all about. I have two use cases from my own work: TrueType fonts, and Mac HFS+ file systems. Both of these are big-endian file formats that need to be read into memory and processed, so (FWIW) I would support the POD approach. Currently, I can't use the code as-is because of the need to use the types in unions. References: http://lists.boost.org/Archives/boost/2000/03/2495.php http://lists.boost.org/Archives/boost/2006/05/105621.php http://lists.boost.org/Archives/boost/2006/06/105695.php http://lists.boost.org/Archives/boost/2006/06/105779.php http://lists.boost.org/Archives/boost/2006/06/105968.php http://lists.boost.org/Archives/boost/2006/06/106655.php http://lists.boost.org/Archives/boost/2006/07/108125.php http://lists.boost.org/Archives/boost/2006/07/108202.php --Neil

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[Phoenix] Review ended September 30th
by Hartmut Kaiser 01 Oct '08

01 Oct '08

Hi all, just a (last) reminder for all of you still wanting to submit a review. The official review period is over, but since I'm going prepare the review summary this weekend only anyway - you still have a day or two. Regards Hartmut Review Manager

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Phoenix and perfect forwarding
by Mathias Gaunard 01 Oct '08

01 Oct '08

Compilers are starting to support rvalue references. Wouldn't it be pertinent to use that to implement perfect forwarding, if available? Phoenix could surely benefit from that.

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