1 #ifndef __JLANG__JRESOLVE__ 
    2 #define __JLANG__JRESOLVE__ 
   10 namespace JPP { 
using namespace JLANG; }
 
   20     template<
class U>   
static auto exists(U*)  -> decltype(
sizeof(U) >= 0);
 
   21     template<
typename>  
static auto exists(...) -> std::false_type;
 
   24     static const bool value = std::is_same<bool, decltype(exists<T>(0))>
::value;   
 
Test existence of class T. 
 
static auto exists(U *) -> decltype(sizeof(U) >=0)
 
static const bool value
true if an implementation of class T exists; else false