Re: [Boost-bugs] [Boost C++ Libraries] #4623: at() member function to ordered_index/hashed_index

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #4623: at() member function to ordered_index/hashed_index
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2010-09-05 18:12:13

#4623: at() member function to ordered_index/hashed_index
--------------------------------------------------------+-------------------
  Reporter:  Akira Takahashi <faithandbrave@…>          |       Owner:  joaquin    
      Type:  Patches                                    |      Status:  new        
 Milestone:  To Be Determined                           |   Component:  multi_index
   Version:  Boost 1.44.0                               |    Severity:  Problem    
Resolution:                                             |    Keywords:             
--------------------------------------------------------+-------------------

Comment (by joaquin):

 Hello Akira,

 ordered indices do not implement `at()` because their interface is
 modelled after that of `std::set`, not `std::map`. Your proposed
 implementation of an `at()` member function is ''not'' consistent
 with the one `std::map` provides:
 {{{
 template<class Key, class T,...>
 class map{
   ...
   const T& at(const key_type& x) const;
 }
 }}}
 Note that `std::map::at` returns a reference to '''`T`''', not
 a reference to '''`value_type`''' as you're doing. Translating this
 to the Boost.MultiIndex realm would imply returning a reference
 to the part of `value_type` that is not the key, which in
 general is not possible (it is possible in the case of
 `std::map` because `value_type` is `std::par<const Key,T>` and
 hence the key is nicely separated from the rest of the value).

 Closing this as a non-problem.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/4623#comment:1>
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