MSVC STL vector::operator[]

    _NODISCARD const_reference operator[](size_type _Off) const noexcept /* strengthened */ {
#if _CONTAINER_DEBUG_LEVEL > 0
        _STL_VERIFY(_Off < this->_Mysize, "vector<bool> subscript out of range");
#endif // _CONTAINER_DEBUG_LEVEL > 0

        const_iterator _It = begin();
        _It._Advance(_Off);
        return *_It;
    }

    _NODISCARD reference operator[](size_type _Off) noexcept /* strengthened */ {
#if _CONTAINER_DEBUG_LEVEL > 0
        _STL_VERIFY(_Off < this->_Mysize, "vector<bool> subscript out of range");
#endif // _CONTAINER_DEBUG_LEVEL > 0

        iterator _It = begin();
        _It._Advance(_Off);
        return *_It;
    }