Check at compile-time is a template type a vector

Question

I can imagine the following code:

template  class X
{
  public:
   T container;

   void foo()
   {
      if(is_vector(T))
         contain         


        

Answer 1

If you use constexpr if, you were doing it right. This C++17 code compiles:

#include 
#include 
#include 
#include 

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

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


template 
class X
{
  public:
   T container;

   void foo()
   {
      if constexpr(is_vector::value){
        std::cout << "I am manipulating a vector" << std::endl;
        // Can access container.push_back here without compilation error
      }
      else {
         std::cout << "I am manipulating something else" << std::endl;
      }
   }
};

int main() {
    X> abc;
    abc.foo(); // outputs "I am manipulating a vector"

    X> def;
    def.foo(); // outputs "I am manipulating something else"
}