#include <iostream>
#include <boost/utility/enable_if.hpp>
#include <boost/static_assert.hpp>

// Has_hello<T>::value is true if T has a hello function.
template<typename T>
struct has_hello {
  typedef char yes[1];
  typedef char no [2];
  template <typename U> struct type_check;
  template <typename U> static yes &chk(type_check<char[sizeof(&U::hello)]> *);
  template <typename  > static no  &chk(...);
  static const bool value = sizeof(chk<T>(0)) == sizeof(yes);
};

template<typename T>
void doSomething(T const& t,
                 typename boost::enable_if_c<has_hello<T>::value>::type* = 0
                 ) {
  return t.hello();
}

// Would need another doSomething` for types that don't have hello().

struct Foo {
  void hello() const {
    std::cout << "hello" << std::endl;
  }
};

// This check is ok:
BOOST_STATIC_ASSERT(has_hello<Foo>::value);

int main() {
  Foo foo;
  doSomething<Foo>(foo);
}