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

An alternative worth considering is to detect the presence of the push_back function using SFINAE. This is slightly more generic since it'll translate to other containers that implement push_back.

template
struct has_push_back
{
    template
    static std::true_type test(
        decltype((void(U::*)(const typename U::value_type&)) &U::push_back)*);

    template
    static std::false_type test(...);

    typedef decltype(test(0)) type;
    static constexpr bool value = 
        std::is_same::value;
};

Note that it currently only detects push_back(const T&) and not push_back(T&&). Detecting both is a little more complicated.

Here's how you make use of it to actually do the insert.

template
void push_back_impl(C& cont, const T& value, std::true_type) {
    cont.push_back(value);
}

template
void push_back_impl(C& cont, const T& value, std::false_type) {
    cont.insert(value);
}

template
void push_back(C& cont, const T& value) { 
    push_back_impl(cont, value, has_push_back::type());
}

std::vector v;
push_back(v, 1);

std::set s;
push_back(s, 1);

Honestly, this solution became a lot more complicated then I originally anticipated so I wouldn't use this unless you really need it. While it's not too hard to support const T& and T&&, it's even more arcane code that you have to maintain which is probably not worth it in most cases.