Re: [Boost-bugs] [Boost C++ Libraries] #5146: Assertion fails in visitation_impl.hpp with nested variants

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #5146: Assertion fails in visitation_impl.hpp with nested variants
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2013-12-10 15:02:54

#5146: Assertion fails in visitation_impl.hpp with nested variants
-------------------------------------+-------------------------------------
  Reporter:  Florian Goujeon         |      Owner:  ebf
  <flo.goujeon@…>                    |     Status:  new
      Type:  Bugs                    |  Component:  variant
 Milestone:  To Be Determined        |   Severity:  Problem
   Version:  Boost 1.45.0            |   Keywords:  variant assert
Resolution:                          |  assertion nested
-------------------------------------+-------------------------------------

Comment (by apolukhin):

 This looks more like a `ptr_to_test_variant` issue, not variant's one.

 Take a look at this code:
 {{{
   const ptr_to_test_variant& direct_ptr_to_ptr_to_tv1 =
 get<ptr_to_test_variant>(ptr_to_ptr_to_tv1);
   ptr_to_ptr_to_tv1 = direct_ptr_to_ptr_to_tv1.pointed_test_variant();
 }}}

 You've got the chain: {{{ ptr_to_ptr_to_tv1 -> direct_ptr_to_ptr_to_tv1 ->
 unnamed }}}

 Then you try to do the following: {{{ ptr_to_ptr_to_tv1 = unnamed; }}}

 Before assigning anything to `ptr_to_ptr_to_tv1` it will delete the data
 it owns:
 {{{
 delete direct_ptr_to_ptr_to_tv1;
 delete unnamed;
 }}}

 And only after that will attempt to do the assignment, but `delete
 unnamed` is already called.

 Much better solution would be to modify code of `ptr_to_test_variant`,
 (you do know that loops are possible, so make small trick to workaround
 such cases):

 {{{
 ptr_to_test_variant&
 ptr_to_test_variant::operator=(const ptr_to_test_variant& rhs)
 {
   test_variant* tmp_ptr = pointed_test_variant_;
   pointed_test_variant_ = new test_variant(*rhs.pointed_test_variant_);
   // Even if there was a loop, data is copied and new
 pointed_test_variant_
   // does not depends on old data at all. We are free to delete the old
 data.
   delete tmp_ptr;
   return *this;
 }
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/5146#comment:3>
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