Detecting whether a class has a specific member function at compile-time:

template<typename T, typename = void>
struct has_serialize : std::false_type {};

template<typename T>
struct has_serialize<T, std::void_t<decltype(std::declval<T>().Serialize())>> : std::true_type {};

// Usage
static_assert(has_serialize<MyPacket>::value, "MyPacket must implement Serialize()");

std::void_t maps any valid type expression to void. If T.Serialize() is invalid, SFINAE drops the specialization cleanly without compiler errors!

std::void_t made writing custom type traits so much simpler in C++17 compared to the old sizeof trick.

C++20 concepts superseded void_t for new code, but understanding void_t is vital for maintaining existing high-performance libraries.