November 2001 - Boost-users

RE: [Boost-Users] question about any class ...
by scleary＠jerviswebb.com 10 Nov '01

10 Nov '01

> any is really a powerful class, but sometimes I would also be > able to know directly the type stored into it without 'guessing', for > example to use it in template code. > What I would like to have is something as > > type_info::real_type for the value hidden into any (not legal > C++, maybe > legal C++0x ?), This actually wouldn't help you, still. How would the declaration look? typeof() wouldn't work, either... > or, alternatively, virtual template functions (again not > legal C++) to be > able to write generic > code depending on both hidden value's type and types 'from the outside > world' (sorry cannot explain it better :-( than this) I have run into this same problem. To re-phrase it, Gianni is trying to do an "operation" on a contained value. 'any' supports the "operations" of copying and destruction as-is; manual modification of 'any' could support other "operations" (this is what Gianni means when he talks about "visiting" the any class, below): any { ... void f() { if (content) content->f(); } }; any::placeholder { ... virtual void f() = 0; }; any::holder<...> ... { ... virtual void f() { held.f(); } }; The problem is how to do this generically (i.e., provide a solution for any "operation"). Another way of looking at this is to force 'any' to call a function that is overloaded on the type of the contained value. Strictly speaking, this isn't possible because 'any' makes the compile-time info into run-time info. > I have tried various approaches, but if I 'visit' the any > class adding a > virtual function to reach hidden value I loose generic type > information > (lack of virtual template functions) from the outside while from the > outside of any > I cannot obtain directly the type of the hidden value ... > > is there a way to do the above ? I have not been successful. Again, 'any' changes compile-time information into run-time information, and to go the other way is just not possible in this language. You could take a "nasty-hack" approach, if you *really* wanted to: 1) Add an 'any_base' class with a virtual function 2) Extend 'any' to return an 'any_base *' referring to the held value, using C-cast notation (derived-to-base when possible, reinterpret when not) 3) Derive your held value types from a common base class 'my_base', which was derived from 'any_base'; add the operations you want to perform to 'my_base' 4) Call the 'any' function returning 'any_base *', downcasting it to 'my_base'. This will result in undefined behaviour if the contained value is not actually derived from 'my_base' (because of the reinterpret_cast behaviour in step 2) I *think* that will work (never tried it). Messy, though, and IMO not generic enough to mess with. Alternatively, you could: 1) Visit 'any'/'any::placeholder'/'any::holder' to provide: void any::action(any which) { content->action(which); } virtual void any::holder::action(any which) { any_action(held, which); } 2) Declare a function 'any_action(T, any)', where the any parameter designates which "operation" to perform. Overloading is then possible on T. Also, where T is a user-defined type, Koenig lookup can be used (abused?) to create different (non-overlapping) sets of "operations". Just some thoughts. Again, I've never tried it. -Steve

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question about any class ...
by Gianni Luciani 10 Nov '01

10 Nov '01

Hi, any is really a powerful class, but sometimes I would also be able to know directly the type stored into it without 'guessing', for example to use it in template code. What I would like to have is something as type_info::real_type for the value hidden into any (not legal C++, maybe legal C++0x ?), or, alternatively, virtual template functions (again not legal C++) to be able to write generic code depending on both hidden value's type and types 'from the outside world' (sorry cannot explain it better :-( than this) I have tried various approaches, but if I 'visit' the any class adding a virtual function to reach hidden value I loose generic type information (lack of virtual template functions) from the outside while from the outside of any I cannot obtain directly the type of the hidden value ... is there a way to do the above ? Gianni Luciani

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Re: any question
by Kevlin Henney 09 Nov '01

09 Nov '01

> From: Thomas Matelich <toms-mailing-lists(a)home.com> > >In the docs, it uses a function called any_ptr, but I don't think it >exists. Could someone please explain? Yes, nothing more elaborate than a typo, I'm afraid! Should be any_cast. Kevlin ____________________________________________________________ Kevlin Henney phone: +44 117 942 2990 mailto:kevlin@curbralan.com mobile: +44 7801 073 508 http://www.curbralan.com fax: +44 870 052 2289 Curbralan: Consultancy + Training + Development + Review ____________________________________________________________

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casting shared_ptr while preserving use_count..
by John Liberty 09 Nov '01

09 Nov '01

I'd like to essentially downcast (to derived) from a base class with virtual methods while preserving (and incrementing) the use_count.. for an upcast, I can simply assign a shared_ptr<Child> to shared_ptr<Parent>. But for the downcast, I need to incorporate a dynamic_cast<childType> to get what I want.. With an older compiler that didn't like member templates, the boost conf would leave the internal pointer and use count as public, so I wrote my own casting function.. However, the newer compiler doesn't give this public access, so I may be stuck without modifying the header... any thoughts?

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How to build the latest release?
by Sinan 08 Nov '01

08 Nov '01

No matter what I try, ( I set JAMBASE, specified boost-base.jam etc... I always get the following error kanita% jam -f./tools/build/allyourbase.jam -sTOOLS="suncc" ./tools/build/allyourbase.jam: line 1608: syntax error at keyword ( don't know how to make all ...found 1 target... ...can't find 1 target... kanita% Line 1608 is the one that says: rule remember-binding ( target : bound-path ) { gBINDING($(target)) = $(bound-path) ; } ... How do I make jam understand the extended syntax ? ( Using FTjam 2.3.5 ...) Sinan Karasu ---------- # (C) Copyright David Abrahams 2001. Permission to copy, use, # modify, sell and distribute this software is granted provided this # copyright notice appears in all copies. This software is provided # "as is" without express or implied warranty, and with no claim as # to its suitability for any purpose. # compute directories for invoking WS6U2 WS6U2_BIN_DIRECTORY ?= $(WS6U2_ROOT_DIRECTORY)$(SLASH)bin ; WS6U2_BIN_DIRECTORY ?= "" ; # Don't clobber tool names if WS6U2_ROOT_DIRECTORY not set WS6U2_INCLUDE_DIRECTORY ?= $(WS6U2_ROOT_DIRECTORY)$(SLASH)include ; WS6U2_STDLIB_DIRECTORY ?= $(WS6U2_ROOT_DIRECTORY)$(SLASH)lib ; flags cc LINKFLAGS <runtime-link>static : -Bstatic ; flags cc CFLAGS <debug-symbols>on : -g ; flags cc LINKFLAGS <debug-symbols>on : -g ; flags cc CFLAGS <optimization>off : -xO0 ; flags cc CFLAGS <optimization>speed : -xO4 ; # Other optimizations we might want for WS6U2 # # flags cc CFLAGS <optimization>space : -xO2 ; flags cc CFLAGS <inlining>off : -xinline=no%func ; flags cc CFLAGS <inlining>on : -xinline=%auto ; flags cc CFLAGS <inlining>full : -xinline=%auto ; flags cc CFLAGS <profiling>on : -xpg ; flags cc LINKFLAGS <profiling>on : -xpg ; flags cc DEFINES <define> ; flags cc UNDEFS <undef> ; flags cc HDRS <include> ; flags cc STDHDRS : $(WS6U2_INCLUDE_DIRECTORY) ; flags cc STDLIBPATH : $(WS6U2_STDLIB_DIRECTORY) ; flags cc CFLAGS <shared-linkable>true : -KPIC ; flags cc LINKFLAGS <shared-linkable>true : -KPIC ; flags cc LINKFLAGS <target-type>DLL : -G ; flags cc LIBPATH <library-path> ; flags cc NEEDLIBS <library-file> ; flags cc FINDLIBS <find-library> ; #### Link #### rule Link-action { # This will appear before the import library name when building a DLL, but # will be "multiplied away" otherwise. The --exclude-symbols directive # proved to be neccessary with some versions of Cygwin. ##sik IMPLIB_COMMAND on $(<) = "-Wl,--exclude-symbols,_bss_end__:_bss_start__:_data_end__:_data_start__ -Wl,--out-implib," ; # IMPLIB_COMMAND on $(<) = "-Wl,--out-implib," ; cc-Link-action $(<) : $(>) ; } # for cc, we repeat all libraries so that dependencies are always resolved actions cc-Link-action bind NEEDLIBS { $(WS6U2_BIN_DIRECTORY)CC $(IMPLIB_COMMAND)$(<[2]) $(LINKFLAGS) -o "$(<[1])" -L$(LIBPATH) -L$(STDLIBPATH) "$(>)" "$(NEEDLIBS)" "$(NEEDLIBS)" -l$(FINDLIBS) -znodefs } # older actions # $(WS6U2_BIN_DIRECTORY)dlltool -e $(<[1]:S=:D=:G=) -l "$(<[2])" "$(>)" # $(WS6U2_BIN_DIRECTORY)CC $(LINKFLAGS) -L$(STDLIBPATH) "$(>)" "$(NEEDLIBS)" "$(NEEDLIBS)" -o "$(<[1])" #### Cc ##### rule Cc-action { cc-Cc-action $(<) : $(>) ; } actions cc-Cc-action { $(WS6U2_BIN_DIRECTORY)cc -c -U$(UNDEFS) -D$(DEFINES) $(CFLAGS) -I$(BOOST_ROOT) -I"$(HDRS)" -I"$(STDHDRS)" -o "$(<)" "$(>)" } #### C++ #### rule C++-action { cc-C++-action $(<) : $(>) ; } actions cc-C++-action { $(WS6U2_BIN_DIRECTORY)CC -c -U$(UNDEFS) -D$(DEFINES) $(CFLAGS) $(C++FLAGS) -I$(BOOST_ROOT) -I"$(HDRS)" -I"$(STDHDRS)" -o "$(<)" "$(>)" } #### Archive #### rule Archive-action { cc-Archive-action $(<) : $(>) ; } actions updated together piecemeal cc-Archive-action { ar ru "$(<)" "$(>)" } [Non-text portions of this message have been removed]

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any question
by Thomas Matelich 08 Nov '01

08 Nov '01

In the docs, it uses a function called any_ptr, but I don't think it exists. Could someone please explain? -- Thomas O Matelich Senior Software Designer Zetec, Inc. matelich(a)home.com tmatelich(a)zetec.com

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Boost release 1.25.1 now available
by Beman Dawes 07 Nov '01

07 Nov '01

Boost release 1.25.1 is now available at www.boost.org: * Boost Build System: Continued improvements. * Config Library: Continued refinements. * Graph Library: Final cleanup for upcoming the Boost Graph Library book. * Thread Library: Minor fixes - tests now pass on most Win32 and POSIX systems including Linux and Solaris. Semaphore removed as too error prone. * Function Library: direct support for member function pointers and documentation updates. * Boost-Users mailing list has been created to address topics of interest to users of Boost libraries. * Boost Wiki web added. Provides a place for Boost users to openly discuss and document the use of Boost libraries. It is not officially maintained by Boost developers. This release uses a new ftp program for updating the web site; the program used in the past was prone to get confused about dates, and didn't recover gracefully from network or server errors. Please let me know if you spot any out-of-date web pages on the site. --Beman

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Boost-Users announcement in 1.25.1
by Douglas Gregor 02 Nov '01

02 Nov '01

Hello all, We should announce the existence of the Boost-Users group in the 1.25.1 release of Boost. I've added a bullet to the "Latest News" entry for the release (just check index.htm in the top level of CVS). My two questions are: - Is there a more precise goal statement that should be in the announcement? (i.e., more precise that "address topics of interest to users of Boost libraries", which is intentionally vague) - Should we mention the Wiki? (with the usual not-Boost-moderated disclaimer) Doug

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