[Boost-bugs] [Boost C++ Libraries] #8749: Accessing type of insert<map<>, pair<A, B> >::type discards inserted elements

Subject: [Boost-bugs] [Boost C++ Libraries] #8749: Accessing type of insert<map<>, pair<A, B> >::type discards inserted elements
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2013-06-30 22:04:35

#8749: Accessing type of insert<map<>, pair<A,B> >::type discards inserted
elements
------------------------------+-----------------------
 Reporter:  guylaingreer@…    |      Owner:  agurtovoy
     Type:  Bugs              |     Status:  new
Milestone:  To Be Determined  |  Component:  mpl
  Version:  Boost 1.52.0      |   Severity:  Problem
 Keywords:                    |
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 The following code sample illustrates the problem

     typedef insert<map<>, pair<int, int> >::type little_map;

     BOOST_STATIC_ASSERT(size<little_map>::value == 1); /* Success */
     BOOST_STATIC_ASSERT(size<little_map::type>::value == 1); /* Failure */

 I have traced the problem to the file boost/mpl/map/aux_/item.hpp in the
 class definition of m_item.  m_item derives from Base (which is a map<...>
 type) but does not define a "typedef m_item type;" to act as a unary
 metafunction returning itself.  The result is that Base::type is found
 instead which means that m_item acts as a unary metafunction returning a
 map with all the inserted elements removed.  The class m_item_ at the
 bottom of the file properly defines a "typedef m_item_ type;" which
 strengthens my belief that it missing from m_item is a bug.

 The solution, quite staightforwardly is to simply add the line "typedef
 m_item type;" to the class' definition.

 It should be noted that I am running version 1.48 of Boost, but have
 checked http://www.boost.org/doc/libs/1_52_0/boost/mpl/map/aux_/item.hpp

 and it still lacks the define so I'm convinced that this problem will
 still be there when I download the latest version of boost.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/8749>
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