C++: What is SFINAE in C++?

1#include <type_traits>
2
3// Enable if T has begin/end (is iterable)
4template<typename T>
5auto print_container(const T& container) ->
6    std::enable_if_t<
7        std::is_same_v<
8            decltype(std::declval<T>().begin()),
9            decltype(std::declval<T>().end())
10        >
11    >
12{
13    for (const auto& item : container) {
14        std::cout << item << " ";
15    }
16    std::cout << "\n";
17}
18
19// Fallback for non-iterable
20template<typename T>
21void print_container(const T& value) {
22    std::cout << value << "\n";
23}
24
25int main() {
26    print_container(std::vector<int>{1, 2, 3});  // OK
27    print_container(42);  // Fallback
28}

1template<typename T>
2void print(const T& value) {
3    if constexpr (std::is_integral_v<T>) {
4        std::cout << "Integer: " << value << "\n";
5    } else if constexpr (std::is_floating_point_v<T>) {
6        std::cout << "Float: " << value << "\n";
7    } else {
8        std::cout << "Other: " << value << "\n";
9    }
10}

1template<std::integral T>
2void print(T value) {
3    std::cout << value << "\n";
4}