[Boost-bugs] [Boost C++ Libraries] #9944: Regression test relies on undefined compiler behavior

Subject: [Boost-bugs] [Boost C++ Libraries] #9944: Regression test relies on undefined compiler behavior
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2014-04-23 18:24:48

#9944: Regression test relies on undefined compiler behavior
------------------------------+--------------------------------
 Reporter:  chris.cooper@…    |      Owner:  grafik
     Type:  Bugs              |     Status:  new
Milestone:  To Be Determined  |  Component:  Regression Testing
  Version:  Boost 1.54.0      |   Severity:  Problem
 Keywords:                    |
------------------------------+--------------------------------
 libs/utility/numeric_traits_test.cpp generates values
 complement_traits<Number>::min using a clever recursive template, but that
 template relies on left-shifting a negative value, and according to the
 C++11 standard that’s a no-no (“the behavior is undefined”) which means
 it’s not a constant expression, which means it can’t be calculated at
 compile time, which means the BOOST_STATIC_ASSERT in line 332 won’t
 compile, saying “static_assert expression is not an integral constant
 expression” (I’m using clang++).

 The only use for the clever templates, as the comment in the file says, is
 for "platforms without <limits> support" so my proposed fix is:

 #ifndef BOOST_NO_LIMITS
 template <class Number> struct complement_traits
 {
     BOOST_STATIC_CONSTANT(Number, min =
 std::numeric_limits<Number>::min());
     BOOST_STATIC_CONSTANT(Number, max =
 std::numeric_limits<Number>::max());
 };
 #else
 [SNIP] All of the other template definitions for complement_traits,
 complement_traits_aux, etc.
 #endif

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/9944>
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