How does subscripting multiple times work for std::array even though all operator[]returns is a reference, without using any proxy-objects (as shown here)?
Example:
#include <iostream>
#include <array>
using namespace std;
int main()
{
array<array<int, 3>, 4> structure;
structure[2][2] = 2;
cout << structure[2][2] << endl;
return 0;
}
How/why does this work?
You simply call structure.operator[](2).operator[](2), where the first operator[] returns a reference to the third array in structure to which the second operator[] is applied.
Note that a reference to an object can be used exactly like the object itself.
As you say, structure[2] gives a reference to an element of the outer array. Being a reference, it can be treated exactly as if it were an object of the same type.
That element is itself an array (array<int,3>), to which a further [] can be applied. That gives a reference to an element of the inner array, of type int.
array<array<T, N>, M>you literally have an array of arrays, so subscripting the outer object returns a reference to an array, which you can then subscript. No proxy needed, because this case is much simpler!int*p, you can computep+6+2. Same thing.