[Boost-bugs] [Boost C++ Libraries] #5141: class template 'value' (bind.hpp) can corrupt compilability of sound code

Subject: [Boost-bugs] [Boost C++ Libraries] #5141: class template 'value' (bind.hpp) can corrupt compilability of sound code
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2011-01-29 22:48:44

#5141: class template 'value' (bind.hpp) can corrupt compilability of sound code
-------------------------------------------------+--------------------------
 Reporter:  jofaber                              |       Owner:  pdimov 
     Type:  Bugs                                 |      Status:  new    
Milestone:  To Be Determined                     |   Component:  bind   
  Version:  Boost 1.46.0                         |    Severity:  Problem
 Keywords:  unexpected compilation dependencies  |  
-------------------------------------------------+--------------------------
 I encountered the following situation. For a new project I combined some
 code like:
 {{{
 #include <boost/my_lib/my_robust_portable_code.hpp>
 }}}

 with some other code
 {{{
 #include <boost/malicious/side_effect_code.hpp>
 #include <boost/my_lib/my_robust_portable_code.hpp>
 }}}
 with the effect, that `my_robust_portable_code.hpp` did not compile
 anymore. Although I found a fix, applicable to
 `my_robust_portable_code.hpp`, I think that such a
 `<boost/malicious/side_effect_code.hpp>` should generally not be
 acceptable for independent components of boost.

 In the concrete case `<boost/tread.hpp>` has this malicious potential to
 confuse msvc-[8..10] when it preceded some of my `boost/icl` files.
 `<boost/tread.hpp>` has the potential to break the code of any other boost
 library and any user code. As the example below shows the corrupted code
 is not extremely nuts and might occur else were.

 Fortunately I was able to locate the problem:

 It's at boost/bind/bind.hpp(112):
 {{{
 namespace _bi{
 ...
 template<class T> class value { ... };
 ...
 } //namespace _bi
 }}}

 This is a minimal program to demonstrate how `class value` can confuse
 msvc:
 {{{
 #include <boost/config.hpp>
 //--- from boost/bind/bind.hpp(112)
 namespace _bi{
     template<class T> class value{};
 }

 //--- affected code ---------------------------------------
 template <class Type> struct some_attribute
 {
     BOOST_STATIC_CONSTANT(int, value = 0);
 };

 template <class Type> struct some_predicate
 {
     BOOST_STATIC_CONSTANT(bool,
         value = ( some_attribute<Type>::value  < 0)
                 //error C2059: syntax error : ')'
                 //IF class template value defined before
         );
 };
 }}}

 Although I frankly don't know, how exactly msvc is derailed, it seems to
 have problems with `value` in
 {{{
 some_attribute<Type>::value  < 0
 }}}
 a construction that is extremely frequent due to meta programming
 conventions introduced by Dave's and Aleksey's `boost::mpl`. So for a fix
 I tried to rename `class value` by something else like `class _value`.
 Fortunately this is possible, because the class template is a local
 implementation object used in `boost/bind/bind.hpp` only.

 After renaming, I successfully ran all tests from boost/bind. Find the
 patch file attached.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/5141>
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