What is useful about a reference-to-array parameter?

Question

I recently found some code like this:

typedef int TenInts[10];
void foo(TenInts &arr);

What can you do in the body of foo()

Answer 1

You can write a function template to find out the size of an array at compile time.

template
size_t array_size(E(&)[size])
{
    return size;
}

int main()
{
    int test[] = {2, 3, 5, 7, 11, 13, 17, 19};
    std::cout << array_size(test) << std::endl; // prints 8
}

No more sizeof(test) / sizeof(test[0]) for me ;-)