C++11模板元编程-std::enable_if示例详解

template
struct enable_if;

template
struct enable_if {};
 
template
struct enable_if { typedef T type; };

#include 

// enable_if example: two ways of using enable_if
#include 
#include 

// 1. the return type (bool) is only valid if T is an integral type:
template 
typename std::enable_if::value,bool>::type
 is_odd (T i) {return bool(i%2);}

// 2. the second template argument is only valid if T is an integral type:
template ::value>::type>
bool is_even (T i) {return !bool(i%2);}

int main() {

 short int i = 1;  // code does not compile if type of i is not integral

 std::cout <

#include 
#include 
#include 

template 
struct is_smart_pointer_helper : public std::false_type {};

template 
struct is_smart_pointer_helper > : public std::true_type {};

template 
struct is_smart_pointer_helper > : public std::true_type {};

template 
struct is_smart_pointer_helper > : public std::true_type {};

template 
struct is_smart_pointer : public is_smart_pointer_helper::type> {};

template 
typename std::enable_if::value,void>::type check_smart_pointer(const T& t)
{
  std::cout <<"is smart pointer" <
typename std::enable_if::value,void>::type check_smart_pointer(const T& t)
{
  std::cout <<"not smart pointer" < pp(new int(2));
  std::unique_ptr upp(new int(4));

  check_smart_pointer(p);
  check_smart_pointer(pp);
  check_smart_pointer(upp);
  
  return 0;
}