Method iterator_valid

common/unordered_inline_set.h:160–162

    iterator begin() const noexcept { return ((SparseArray*)this)->_begin(); }
    iterator end() const   noexcept { return {(SparseArray*)this, _capacity}; }
    bool iterator_valid(iterator it) const noexcept {
        return it._a == this && it._i <= capacity();
    }

    const T& operator[](size_t i) const {
        return *get(i);