1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
#include <boost/variant.hpp>
#include <typeinfo>
template <typename T>
auto foo(const boost::variant<int, double>& variant, double bar) -> decltype(typeid(T) == typeid(int) ? boost::get<T>(variant) : bar)
{
return typeid(T) == typeid(int) ? boost::get<T>(variant) : bar;
}
int main()
{
const boost::variant<int, double> variant;
foo<int>(variant, 0.5);
}
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
g++-4.8 -std=c++11 -O2 -Wall -pedantic -pthread main.cpp && ./a.out

main.cpp: In instantiation of 'decltype (((typeid(T) == typeid(int)) ? get<T>(variant) : bar)) foo(const boost::variant<int, double>&, double) [with T = int; decltype (((typeid(T) == typeid(int)) ? get<T>(variant) : bar)) = double]':
main.cpp:14:26:   required from here
main.cpp:6:6: sorry, unimplemented: mangling typeid_expr
 auto foo(const boost::variant<int, double>& variant, double bar) -> decltype(typeid(T) == typeid(int) ? boost::get<T>(variant) : bar)
      ^
main.cpp:6:6: sorry, unimplemented: mangling typeid_expr