[Boost-bugs] [Boost C++ Libraries] #8360: Multiplication operator should allow non-commutative version

Subject: [Boost-bugs] [Boost C++ Libraries] #8360: Multiplication operator should allow non-commutative version
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2013-04-01 15:47:10

#8360: Multiplication operator should allow non-commutative version
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 Reporter:  Jaap Eldering <eldering@…>                |       Owner:  daniel_frey
     Type:  Bugs                                      |      Status:  new        
Milestone:  To Be Determined                          |   Component:  operators  
  Version:  Boost 1.53.0                              |    Severity:  Problem    
 Keywords:                                            |  
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 The multipliable2 template in `boost/operators.hpp` is defined with the
 `BOOST_BINARY_OPERATOR_COMMUTATIVE` macro. This macro defines
 multiplication of types T and U in both orders in terms of `T *= U`.

 This assumes that multiplication is commutative, which is not generally
 true. For example when T is a nxn matrix type with double entries and U a
 nxn matrix with integer entries, then `T *= U` makes sense, but
 `operators.hpp` would define `U * T` using `T *= U`. Since matrix
 multiplication is not commutative, this would give wrong results.

 Suggested solution: make `multipliable2` use the NONCOMMUTATIVE macro, or
 add another `multipliable2_nc` template.

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Ticket URL: <https://svn.boost.org/trac/boost/ticket/8360>
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