It's "zero cost abstractions over what you would write by hand". If you argue that anyone doing array access should be doing bounds checks when in doubt, a C++ compiler performing bounds checks would still be considered zero(additional)-cost.
I'm all for better tools to help the compiler figure things out.
Here is an example where I can't communicate the invariants to the compiler:
```
std::vector<int> v;
...
v.push_back(2);
std::sort(v.begin(), v.end());
// no need to check i < size because we know we will find value 2 somewhere in the v.
for (int i = 0; i < v.size(); ++i) {
if (v[i] == 2) return i;
}
```
Note that in C++ you can manually mark code after the loop as unreachable, which would indeed skip the size check.
But that's as bad as not checking bounds in the first place.