[Boost-bugs] [Boost C++ Libraries] #13346: SFINAE-friendly range_value

Subject: [Boost-bugs] [Boost C++ Libraries] #13346: SFINAE-friendly range_value
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2017-12-17 19:53:47

#13346: SFINAE-friendly range_value
------------------------------+-------------------------
 Reporter:  marc.glisse@…     |      Owner:  Neil Groves
     Type:  Feature Requests  |     Status:  new
Milestone:  To Be Determined  |  Component:  range
  Version:  Boost 1.62.0      |   Severity:  Problem
 Keywords:  sfinae            |
------------------------------+-------------------------
 This code compiles:

 {{{
 #include <boost/range/value_type.hpp>
 #include <utility>
 #include <iterator>

 template<class T>
 void f(std::pair<T,T>){}

 template<class T>
 auto f(T) -> typename std::iterator_traits<typename
 boost::range_iterator<T>::type>::value_type {}

 int main(){
   std::pair<int,int> p;
   f(p);
 }
 }}}

 However, if I change the return type to the more readable `typename
 boost::range_value<T>::type`, it now fails to compile because the broken
 typedef in iterator_value is not in the immediate context. The standard
 noticed that this was useful and made iterator_traits SFINAE-friendly, it
 would be nice if boost could do the same for the various range meta-
 functions.

-- 
Ticket URL: <https://svn.boost.org/trac10/boost/ticket/13346>
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