[multiprecision] [detail] [number_base.hpp] Ambiguous partial specialization for canonical_imp

28 Dec 2014

      It looks like boost/multiprecision/detail/number_base.hpp header in one 
of the later trunk versions
has  ambiguous partial specialization problem which Oracle Studio 12.4 
C++ compiler  detects.
It can be also detected by gcc-4.8.2 as small 35 lines  independent test 
case below  made from this header shows.

gcc  -c -std=c++11 t.cc  # gcc-4.8.2 compilation
t.cc:17:62: error: ambiguous class template instantiation for 'struct 
canonical_imp, 
(expression_template_option)1u>, cpp_dec_float<50u>, int_<3> >'

CC  -c -std=c++11 t.cc # Oracle Studio 12.4 C++ compilation
"t.cc", line 17: Error: Ambiguous partial specialization for 
canonical_imp, 
1>, cpp_dec_float<50, int, void>, int_<3>>, canonical_imp> and canonical_imp, Backend, Tag>.

t.cc
==================================
template< bool B> struct enable_if_c{
  typedef bool type;
};
template< int N > struct int_{};
enum expression_template_option {et_on=1};
template  
class number;
template  struct canonical_imp {
  typedef int type;
};
template  struct 
canonical_imp,Backend,Tag> {
  typedef B type;
};
template  struct 
canonical_imp>{
  typedef Val type;
};
template  struct canonical {
  typedef typename canonical_imp>::type type;
};
template struct is_restricted_conversion {
  typedef bool type;
};
template  
class number {
  public:
   number() {}
   template <class V> number(const V& v,typename 
enable_if_c::type,Backend>::value>::type * =0){}
};
template  class cpp_dec_float;
template  class 
cpp_dec_float {
  public: cpp_dec_float() {}
};
template <class RealType> void instantiate(RealType) {}
typedef number, et_on> test_type;
void foo() {
   instantiate(test_type());
}
===============================

Any suggestions how to fix this?

Thanks,

Sergey

Sergey Sprogis

John Maddock

Sergey Sprogis

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