[Boost-bugs] [Boost C++ Libraries] #4009: lexical_cast to multimember object fails

Subject: [Boost-bugs] [Boost C++ Libraries] #4009: lexical_cast to multimember object fails
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2010-03-14 17:33:26

#4009: lexical_cast to multimember object fails
--------------------------------------------------+-------------------------
 Reporter:  Darko Veberic <darko.veberic@…>       |       Owner:  nasonov     
     Type:  Bugs                                  |      Status:  new         
Milestone:  Boost 1.43.0                          |   Component:  lexical_cast
  Version:  Boost 1.40.0                          |    Severity:  Showstopper 
 Keywords:                                        |  
--------------------------------------------------+-------------------------
 According to the documentation, the only relevant requirement for the
 lexical_cast<target>(source) is that the target is input-streamable.
 Having a simple class
 {{{
 struct Foo {
   int fA;
   int fB;
 };
 }}}
 with input operator
 {{{
 istream&
 operator>>(istream& is, Foo& f)
 {
   return is >> f.fA >> f.fB;
 }
 }}}
 should satisfy all the requirements. Nevertheless, the code
 {{{
 const string s = "137 13";
 const Foo f = lexical_cast<Foo>(s);
 }}}
 compiles without any warnings (g++ 4.4.1) but eventually throws a
 bad_lexical_cast exception. Of course, using a non-optimized non-boost
 version of the lexical cast
 {{{
 template<typename T, typename U>
 T
 LexicalCast(const U& u)
 {
   stringstream ss;
   ss << u;
   T t;
   if (ss >> t)
     return t;
   else
     throw bad_lexical_cast();
 }
 }}}
 works fine for the class in the example above. Are there additional
 requirements on the target type that are not mentioned in the
 documentation or is this a really severe bug?

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/4009>
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