trap.cpp

#include <iostream>
#include <type_traits>

#if defined(__unix__)
#include <signal.h>
#include <unistd.h>
#endif

#if (defined(_M_IX86) || defined(__i386__) || defined(_M_IA64) || defined(__ia64__)) && defined(__GNUC__)
#define DEBUG_TRAP()  __asm("int3")
#elif defined(_MSC_VER)
#define DEBUG_TRAP()  __debugbreak()
#elif defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))
#define DEBUG_TRAP() kill(getpid(), SIGTRAP)
#else
#error I dont know how to SIGTRAP on this platform
#endif

template<bool Condition> 
std::enable_if_t<Condition> trap() 
{ 
  DEBUG_TRAP(); 
}

template<bool Condition> std::enable_if_t<!Condition> trap() {}

template<int N> void foo()  
{
  trap< (N<4) >();
  std::cout << N << std::endl;
}

int main()
{
  foo<7>();
  foo<1>();
  foo<3>();
}