[cfe-users] Ambigous function call with template

[Florian Lindner]

Hello,

I have a piece of code that works perfectly with recent versions of g++ but 
fails to compile with clang++. I try to understand why.

ScalarOperations.h:

    template<typename Type>
      typename utils::EnableIf<(not IsVector<Type>::value),
      bool
    >::Type smallerEquals (
      Type lhs,
      Type rhs,
      Type tolerance = NUMERICAL_ZERO_DIFFERENCE);

ScalarOperations.cpph:

template<typename Type>
  inline
  typename utils::EnableIf<not IsVector<Type>::value,
  bool
>::Type smallerEquals (
  Type lhs,
  Type rhs,
  Type tolerance
) {
  return lhs - rhs <= tolerance;
}


this is called from ScalarTest.cpp like that:

#include "code.h"

double a = 1.0;
double b = 2.0;
double eps = 1e-14;
validate (smallerEquals(a, b, eps));

That fails with:

clang++ -o build/debug/tarch/la/tests/ScalarTest.o -c -fPIC -g3 -O0 -DDebug 
-DAsserts -Isrc -Isrc -I/usr/include/openmpi -I/usr/include -
I/usr/include/python2.7 -I/usr/include/python2.7/numpy 
src/tarch/la/tests/ScalarTest.cpp

src/tarch/la/tests/ScalarTest.cpp:53:13: error: call to 'smallerEquals' is 
ambiguous
  validate (smallerEquals(a, b, eps));
            ^~~~~~~~~~~~~
src/tarch/tests/TestMacros.h:45:37: note: expanded from macro 'validate'
#define validate(booleanExpr) if (!(booleanExpr)) { \
                                    ^
src/tarch/la/ScalarOperations.h:77:13: note: candidate function [with Type = 
double]
    >::Type smallerEquals (
            ^
src/tarch/la/ScalarOperations.cpph:79:9: note: candidate function [with Type 
= double]
>::Type smallerEquals (
        ^

Lines 77 resp. 79 are the lines I posted above. If I delete the code in the 
CPPH file it compiles fine but fails at linking (of course).

What is the problem here?

Thanks,
Florian