Effect of subscripting the this pointer

What does this[5] do? Have I invoked some kind of undefined behavior? What about:

std::vector<decltype(this)> foo{this, this + 5u};

Is this useful? I want to know what the effects of pointer arithmetic on this are. Here's a test program:

#include <iostream>
#include <vector>

struct Foo
{
    int n = 1;

    void foo()
    {
        std::vector<decltype(this)> foo{this, this + 5u};
        for (decltype(foo.size()) i = 0; i != foo.size(); ++i)
        {
            std::cout << foo[i]->n << "\n";
        }
    }
};

int main()
{
    Foo{}.foo();
}

/* OUTPUT:
 * 1
 * 0
 */