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)
         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.

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