If your array is unordered then you can just swap the end element down when erasing an element.

From my own code:

template<hxarray_concept_ T_, size_t capacity_>

void hxarray<T_, capacity_>::erase_unordered(const T_* pos_) {

    hxassertmsg(pos_ >= this->data() && pos_ < m_end_, "invalid_iterator");

    if(pos_ != --m_end_) {

        *const_cast<T_*>(pos_) = hxmove(*m_end_);

    }

    m_end_->~T_();

}

This is something I think the std::vector could definitely use.