[Boost-bugs] [Boost C++ Libraries] #12194: Copy assignment on moveable and copyable classes uses wrong type

Subject: [Boost-bugs] [Boost C++ Libraries] #12194: Copy assignment on moveable and copyable classes uses wrong type
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2016-05-12 11:31:32

#12194: Copy assignment on moveable and copyable classes uses wrong type
--------------------------+------------------------
 Reporter:  a.grund@…     |      Owner:  igaztanaga
     Type:  Bugs          |     Status:  new
Milestone:  Boost 1.61.0  |  Component:  move
  Version:  Boost 1.59.0  |   Severity:  Regression
 Keywords:                |
--------------------------+------------------------
 A patch introduced a breaking change to classes that are copyable and
 movable:
 https://github.com/boostorg/move/commit/4f9c2b62fbdcf5995ecf50a2ecf2494048a6696d

 #diff-6a11d48d06dd33c1193ffb3d794787fbR252

 The macro was changed so the {{{TYPE& operator=(TYPE &t)}}} calls the
 assignement operator with a type {{{ const TYPE& }}} instead of {{{ const
 ::boost::rv<TYPE> & }}}

 This change is not described and seems to be a mistake that was not caught
 in the review process. As the macro {{{ BOOST_COPY_ASSIGN_REF }}} still
 expands to the original rv-type a wrong operator might get called. A
 minimum example:


 {{{
 #include <boost/move/move.hpp>
 #include <cassert>

 class Foo{
     BOOST_COPYABLE_AND_MOVABLE(Foo)
 public:
     int i;
     explicit Foo(int val): i(val){}
     Foo(BOOST_RV_REF(Foo) obj): i(obj.i) {}
     Foo& operator=(BOOST_RV_REF(Foo) rhs){ i = rhs.i; return *this; }
     Foo& operator=(BOOST_COPY_ASSIGN_REF(Foo) rhs){ i = rhs.i; return
 *this; }
     template<class OTHER>
     Foo& operator=(const OTHER& rhs){ i = rhs.j; return *this; }
 };

 struct Bar{
     int j;
     explicit Bar(int val): j(val){}
 };

 int main(){
     Foo foo1(1);
     Foo foo2(2);
     Bar bar(3);
     assert(foo1.i == 1);
     assert(foo2.i == 2);
     assert(bar.j == 3);
     foo2 = foo1;
     assert(foo1.i == 1);
     assert(foo2.i == 1);
     foo1 = bar;
     assert(foo1.i == 3);
     return 0;
 }
 }}}

 This compiles and works fine in boost <=1.58 but fails in >=1.59 as the
 template version is called.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/12194>
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