Re: [Boost-bugs] [Boost C++ Libraries] #10133: boost 1.55 breaks fusion map arrays

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #10133: boost 1.55 breaks fusion map arrays
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2014-07-05 15:58:49

#10133: boost 1.55 breaks fusion map arrays
-------------------------------+------------------------
  Reporter:  steven.seeger@…   |      Owner:  djowel
      Type:  Bugs              |     Status:  new
 Milestone:  To Be Determined  |  Component:  fusion
   Version:  Boost 1.55.0      |   Severity:  Regression
Resolution:                    |   Keywords:
-------------------------------+------------------------

Comment (by anonymous):

 After a discussion on the mailing list, it was determined that my use of
 for_each is not correct. The library should not have stepped through each
 item of an array in a fusion map but rather send the whole array as a type
 to the function called on each value. It appears that this has been fixed
 in 1.55.

 I had a discussion on the mailing list with Agustin quoted below:

 > Hi Agustin thanks for your reply. You are correct that what I'm doing is
 not documented. In fact, it doesn't really make sense now that I look at
 it. The for_each should be called on each type. If the type is an array it
 doesn't make sense for a for_each to break down the array. That said,
 there should be some way to specialize operator() in the functor passed to
 it in order to correctly handle array types.

 I missed the part where `for_each` was invoking the callable on each
 element of the array, that is not how it is supposed to be. You are
 right that making a recursive callable is the correct way to obtain that
 behavior.
 --

 This suggests that in reality what I was doing before was actually the
 bug, and that 1.55 has the correct behavior.

 One issue that we did find, however, is that fusion maps with
 std::array<T> types cannot have static initializers with 1.55.

 For example,

      typedef boost::fusion::map<boost::fusion::pair<struct blah, short>,
              boost::fusion::pair<struct bleh, int>,
              boost::fusion::pair<struct foo, std::array<int, 2>>,
              boost::fusion::pair<struct bloog, std::string> > test_t;

      test_t test{1,2, {{3,4}}, "test"};

 This compiles with 1.53 but not 1.55. The {{3, 4}} is the issue.

 Also interestingly enough, I have to put braces around "test" with 1.53
 but not 1.55.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/10133#comment:1>
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