"Unmanaged Constraint"

// This method copies a T reference to a T value via pointer
static unsafe void Copy<T>(ref T src, T* dest) where T : unmanaged => *dest = src;

static unsafe void Test() {
    int dest = 0;
    int src = 3;
    Copy(ref src, &dest);

    Console.WriteLine(dest); // Prints '3'
}