Sample SFINAE examples

sfinae.cpp

#include <iostream>
#include <type_traits>

struct tag1{};
struct tag2{};

enum class Tags {
    type1,
    type2,
};

//template <typename T, std::enable_if<(T::type == Tags::type1), void>>
template <typename T, std::enable_if_t<(T::type == Tags::type1)> * = nullptr>
void lol(T obj)
{
    std::cout << "lol " << (int)T::type << '\n';
}

template <typename T, std::enable_if_t<(T::type == Tags::type2)> * = nullptr>
void lol(T obj)
{
    std::cout << "lol " << (int)T::type << '\n';
}

template <typename T, std::enable_if_t<std::is_same<typename T::tag, tag1>::value, bool> = true>
void display(T obj)
{
    std::cout << "tag1 display\n";
}

 template <typename T, std::enable_if_t<std::is_same<typename T::tag, tag2>::value, bool> = true>
void display(T obj)
{
    std::cout << "tag2 display\n";
}

struct Data1 {using tag = tag1; };
struct Data2 {using tag = tag2; };

struct LolData1 {static constexpr Tags type = Tags::type1; };
struct LolData2 {static constexpr Tags type = Tags::type2; };

int main()
{
    Data1 obj1;
    Data2 obj2;
    display(obj1);
    display(obj2);
    LolData1 data1;
    lol(data1);
    LolData2 data2;
    lol(data2);
}