Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

Returns the i-th resultset (unchecked access).

resultset_view
operator[](
    std::size_t i) const;

this->has_value() == true && i < this->size()

No-throw guarantee.

The returned reference and any other references obtained from it are valid as long as *this is alive. Move operations invalidate references.

Constant.