Re: [Boost-bugs] [Boost C++ Libraries] #13434: index_args_default_compare uses result_type

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #13434: index_args_default_compare uses result_type
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2018-02-02 09:09:34

#13434: index_args_default_compare uses result_type
-------------------------------+-----------------------------------
  Reporter:  gast128@…         |      Owner:  Joaquín M López Muñoz
      Type:  Bugs              |     Status:  new
 Milestone:  To Be Determined  |  Component:  multi_index
   Version:  Boost 1.65.0      |   Severity:  Problem
Resolution:                    |   Keywords:
-------------------------------+-----------------------------------

Comment (by Joaquín M López Muñoz):

 OK, I see. You have to define your user-provided extractor as follows:
 {{{
 template <class PairType>
 struct select1st
 {
     typedef typename PairType::first_type result_type;

     const typename PairType::first_type& operator()(const PairType& cr)
 const
     {
         return cr.first;
     }
 };
 }}}
 I don't consider this a problem in the library, as the requirement that
 the key extractor have `::result_type` is not dependent on the existence
 (or lack thereof) of `std::unary_function`. Closing as invalid.

-- 
Ticket URL: <https://svn.boost.org/trac10/ticket/13434#comment:3>
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