Re: [Boost-bugs] [Boost C++ Libraries] #6711: with unordered_map using interprocess basic_string in shared memory, find and [] are annoying

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #6711: with unordered_map using interprocess basic_string in shared memory, find and [] are annoying
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-03-21 23:00:50

#6711: with unordered_map using interprocess basic_string in shared memory, find
and [] are annoying
----------------------------------+-----------------------------------------
  Reporter:  jdy@…                |       Owner:                                        
      Type:  Feature Requests     |      Status:  closed                                
 Milestone:  To Be Determined     |   Component:  None                                  
   Version:  Boost 1.49.0         |    Severity:  Problem                               
Resolution:  wontfix              |    Keywords:  interprocess, unordered_map, container
----------------------------------+-----------------------------------------

Comment (by danieljames):

 It does, because it can break valid code. Consider this:

 {{{
 #include <cassert>
 #include <functional>

 struct source {};

 struct value {
     value(source&&) {}
 };

 void foo(value const& x) { std::equal_to<value>(x); }

 #if defined(ADD_TEMPLATE)
 template <typename T>
 void foo(T const& x) { std::equal_to<value>(x); }
 #endif

 int main() {
     foo(source());
 }
 }}}

 Note that ADD_TEMPLATE adds a template overload, as you're suggesting.
 Defining ADD_TEMPLATE causes it to fail:

 {{{
 $ g++-mp-4.7 --std=c++0x demo.cpp
 $ g++-mp-4.7 --std=c++0x demo.cpp -DADD_TEMPLATE
 demo.cpp: In instantiation of 'void foo(const T&) [with T = source]':
 demo.cpp:19:17:   required from here
 demo.cpp:15:24: error: invalid initialization of reference of type 'const
 value&' from expression of type 'const source'
 demo.cpp:9:6: error: in passing argument 1 of 'void f(const value&)'
 }}}

 The same could happen if a template overload was added for `find`.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/6711#comment:3>
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