c++ - How does "sizeof" work in this helper for determining array size?

Question

I've found this article that brings up the following template and a macro for getting array size:

template<typename Type, size_t Size>
char ( &ArraySizeHelper(Type( &Array )[Size]) )[Size];
#define _countof(Array) sizeof(ArraySizeHelper(Array))

and I find the following part totally unclear. sizeof is applied to a function declaration. I'd expect the result to be "size of function pointer". Why does it obtain "size of return value" instead?

Answer 1

sizeof is applied to the result of a function call, not a declaration. It therefore gives the size of the return value, which in this case is a reference to an array of chars.

The template causes the array in the return type to have the same number of elements as the argument array, which is fed to the function from the macro.

Finally, sizeof is then applied to a reference to this char array. sizeof on a reference is the same as sizeof on the type itself. Since sizeof(char) == 1, this gives the number of elements in the array.